Method of manufacturing multi-layer printed circuit board

ABSTRACT

An intermediate layer  38  is provided on a die pad  22  of an IC chip  20  and integrated into a multilayer printed circuit board  10 . Due to this, it is possible to electrically connect the IC chip  20  to the multilayer printed circuit board  10  without using lead members and a sealing resin. Also, by providing the intermediate layer  38  made of copper on an aluminum pad  24 , it is possible to prevent a resin residue on the pad  24  and to improve connection characteristics between the die pad  24  and a via hole  60  and reliability.

CROSS REFERENCE OF RELATED APPLICATION

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 from U.S. Ser. No. 11/747,972, filed May 14, 2007,which is a divisional of U.S. Ser. No. 10/380,631, filed Mar. 21, 2003,and a national stage of PCT/JP01/03589, filed Apr. 25, 2001, and furtheris based upon and claims the benefit of priority from the prior JapanesePatent Application Nos. 2000-290231, filed Sep. 25, 2000; 2000-290232,filed Sep. 25, 2000; 2000-382806, filed Dec. 15, 2000; 2000-382807,filed Dec. 15, 2000; 2000-382813, filed Dec. 15, 2000; 2000-382814,filed Dec. 15, 2000.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a semiconductor device such as an ICchip, a semiconductor device manufacturing method, a multilayer printedcircuit board into which a semiconductor device is integrated and amultilayer printed circuit board manufacturing method.

BACKGROUND OF THE INVENTION

An IC chip is electrically connected to a printed circuit board by amounting method such as wire bonding, TAB or flip chip bonding.

In the wire bonding method, an IC chip is die-bonded to a printedcircuit board by adhesive, the pads of the printed circuit board areconnected to the pads of an IC chip by wires such as metallic wires andthen a sealing resin such as a thermosetting resin or a thermoplasticresin is applied to protect the IC chip and the wires.

In the TAB method, the wires referred to as leads are connected in theblock by a solder or the like and then the bumps of an IC chip and thepads of a printed circuit board are sealed by a resin.

In the flip chip bonding method, the pads of an IC chip are connected tothe pads of a printed circuit board through bumps and the gaps betweenthe pads and the bumps are filled with a resin.

In each of these mounting methods, however, the IC chip is electricallyconnected to the printed circuit board through connection lead members(wires, leads or bumps). The lead members tend to be cut off and eroded,thereby breaking the connection of the printed circuit board with the ICchip and causing malfunctions.

Further, in each mounting method, a thermoplastic resin such as an epoxyresin is applied to seal the IC chip so as to protect the IC chip. Ifbubbles are contained at the time of filling the resin, the breakage oflead members, the corrosion of the IC pads and the deterioration ofreliability are derived from the bubbles. To seal members by athermoplastic resin, it is necessary to create resin filling plungersand metallic molds in accordance with the respective members. Inaddition, if a thermosetting resin is employed, it is necessary toselect an appropriate resin for the materials of lead members, solderresist and the like, thereby disadvantageously causing cost increase.

On the other hand, there has been conventionally proposed a techniquefor electrically connecting an IC chip to a printed circuit board byembedding a semiconductor device into a substrate and forming builduplayers on the substrate instead of attaching the IC chip to the exteriorof the printed circuit board (or package substrate) as stated above inJapanese Patent Laid-Open Nos. 9-321408 (or U.S. Pat. No. 5,875,100),10-256429, 11-126978 and the like.

According to Japanese Patent Laid-Open No. 9-321408 (or U.S. Pat. No.5,875,100), a semiconductor device having stud bumps formed on die padsis embedded into a printed circuit board and wirings are formed on thestud bumps to thereby electrically connect the printed circuit board tothe semiconductor device. However, since the stud bumps are onion-shapedand irregular in height, smoothness is deteriorated if an interlayerinsulating layer is formed and electrical connection cannot beestablished even if via holes are formed. Further, since the stud bumpsare provided by bonding one by one, they cannot be provided collectivelyand productivity is thereby disadvantageously lowered.

Japanese Patent Laid-Open No. 10-256429 shows a structure in which asemiconductor device is contained in a ceramic substrate and thesubstrate is electrically connected to the semiconductor device by flipchip bonding. However, ceramic is inferior in outline workability andthe semiconductor device cannot be appropriately contained in theceramic substrate. Besides, the bumps are irregular in height. Due tothis, the smoothness of an interlayer insulating layer is deterioratedand connection characteristic is deteriorated accordingly.

Japanese Patent Laid-Open No. 11-126978 shows a multilayer printedcircuit board wherein an electrical component such as a semiconductordevice is embedded into a gap or containing portion, connected to aconductor circuit and built up through via holes. However, since thecontaining portion is a gap, a positional error tends to occur and thesubstrate cannot be often connected to the pads of the semiconductordevice. Besides, since die pads are directly connected to the conductorcircuit, oxide coats tend to be formed on the respective die pads,thereby disadvantageously increasing insulating resistance.

The present invention has been made to improve the above-statedproblems. It is an object of the present invention to provide asemiconductor device manufacturing method which allows a semiconductordevice to be directly electrical connected to a printed circuit boardwithout using lead members.

Meanwhile, if a semiconductor device is embedded into a printed circuitboard made of resin, then the printed circuit board is warped by heatgenerated in the semiconductor device, internal wirings are cut off andreliability is thereby disadvantageously deteriorated.

The present invention has been made to improve the above-stated problem.It is, therefore, a still further object of the present invention toprovide a multilayer printed circuit board into which a semiconductordevice is integrated and the method of manufacturing the multilayerprinted circuit board.

Furthermore, conventionally, a highly reliable printed circuit boardinto which a semiconductor device is integrated cannot be efficientlymanufactured.

The present invention has been made to improve the above problem. It is,therefore, a still further object of the present invention to provide amanufacturing method capable of efficiently manufacturing a highlyreliable multilayer printed circuit board into which a semiconductordevice is integrated.

Moreover, if a multilayer printed circuit board comprising a substrateinto which a semiconductor device is embedded and contained, is employedas a package substrate, a chip set or the like, the multilayer printedcircuit board can fulfill its behaviors by being electrically connectedto an external substrate (which is a so-called mother board or adaughter board). Due to this, it is necessary to provide BGA's andconductive connection pins (PGA's) on the multilayer printed circuitboard. The BGA's and PGA's are formed by providing solder pads on asolder resist layer on the surface layer of the multilayer printedcircuit board.

However, if a behavioral test or a reliability test is conducted whileproviding solder bumps on the surface layer of a substrate into which asemiconductor device is embedded and electrically connecting thesubstrate to an external substrate, it is discovered that an interlayerinsulating layer, a solder resist layer, an interlayer resin insulatinglayer, a solder resist, solder bumps and the surroundings of the solderbumps (which means solder layers and corrosion resisting metal) arecracked and peeled, that the solder bumps are detached and that thepositions of the solder bumps are slipped. Particularly, cracks occur tothe pads of the semiconductor device and the cracks penetrate theinterlayer insulating layer. Accordingly, it becomes clear that in themultilayer printed circuit board into which the semiconductor device isintegrated, the electrical connection characteristics between solderbumps and conductor circuits is disadvantageously deteriorated and thatthe reliability of the multilayer printed circuit board is deterioratedaccordingly.

The present invention has been made to improve the above-statedproblems. It is, therefore, a still further object of the presentinvention to provide a multilayer printed circuit board or particularlya multilayer printed circuit board into which a semiconductor device isintegrated having high electrical connection characteristics and highreliability.

DISCLOSURE OF THE INVENTION

As a result of dedicated studies, the inventor of the present inventiondevised to form a transition layer on the die pad of a semiconductordevice. Even if the semiconductor device having the transition layer isembedded, stored and contained in a printed circuit board and aninterlayer insulating layer is provided on the semiconductor device andvia holes are formed in the interlayer insulating layer, it is possibleto obtain desired size and shape.

The reason for providing the transition layer on the die pad of an ICchip will be described. The die pad of an IC chip is normally made ofaluminum or the like. If the via holes of an interlayer insulating layerare formed by photo-etching while no transition layer is formed on thedie pad, a resin tends to remain on the surface layer of the pad afterexposure and development. Besides, the pad is discolored due to theadhesion of a development solution. On the other hand, if via holes areformed by laser, there is a possibility of burning the aluminum pad.Also, if via holes are formed under the conditions that the pad is notburned, a resin residue on the pad occurs. In addition, if the IC chipis immersed in an acid, an oxidizer or an etching solution in latersteps or subjected to various annealing steps, the pad of the IC chip isdiscolored and dissolved. Moreover, the pad of the IC chip is formed tohave a diameter of about 40 μm and a via hole is larger in diameter thanthe pad to thereby require a location tolerance. As a result, apositional error and a connection defect tend to occur.

By providing a transition layer made of copper or the like on a die pad,by contrast, a via hole formation defect can be improved to make itpossible to use a solvent and a resin residue on the pad can beprevented. Also, even if the IC chip is immersed in an oxide, anoxidizer or an etching solution in later steps or subjected to variousannealing steps, the pad is not discolored or dissolved. This allowsimproving the connection characteristics between the pad and the viahole and reliability. Moreover, by interposing the transition layerhaving a larger diameter than that of the die pad of the IC chip, it ispossible to ensure connecting the via hole to the pad. It is preferablethat the transition layer is equal to or larger than a via hole diameteror a location tolerance.

Furthermore, since the transition layer is formed, the operation testand electrical test of the semiconductor device can be easily conductedbefore or after embedding, containing and storing the IC chip which is asemiconductor device in a printed circuit board. This is because thetransition layer larger than the pad is formed and a test probe pin canbe contacted with the IC chip more easily. As a result, it is possibleto determine whether a product is good or defective in advance and toimprove productivity and cost effectiveness. Besides, the pad is notlost or damaged by the probe.

Thus, by forming the transition, the IC chip which is a semiconductordevice can be appropriately embedded, contained and stored in theprinted circuit board. Namely, the semiconductor device having thetransition layer may be also referred to as a semiconductor device forembedding, containing and storing the printed circuit board.

The transition layer is constituted by forming a thin film layer on thedie pad and a thickening layer on the thin film layer. The transitionlayer can be formed to comprise at least two layers.

The multilayer printed circuit board functions per se. In some cases,BGA's, solder bumps or PGA's (conductive connection pins) may beprovided to connect the multilayer printed circuit board to a motherboard or a daughter board serving as an external substrate so that themultilayer printed circuit board functions as a package substrate for asemiconductor device. In addition, with this constitution, wiringlengths can be shortened and loop inductance can be reduced comparedwith a case of connecting the multilayer printed circuit board to theexternal substrate by a conventional mounting method.

Now, a transition layer defined in the present invention will bedescribed.

Since the transition layer directly connect an IC chip, which is asemiconductor device, to a printed circuit board without using aconventional IC chip mounting technique, the transition layer signifiesan intermediate layer. The transition layer is characterized by beingformed out of two or more metallic layers or by being formed to belarger than the die pad of the IC chip which is the semiconductordevice. This allows electrical connection characteristics and alignmentefficiency to be improved and processing a via hole by laser orphoto-etching without damaging the die pad. Due to this, it is possibleto ensure embedding, containing, storing and connecting the IC chip inand to the printed circuit board. Besides, it is possible to directlyform a metal serving as the conductor layer of the printed circuit boardon the transition layer. The conductor layer is exemplified by the viahole of an interlayer resin insulating layer or a through hole on asubstrate.

As a resin substrate into which an electronic component such as an ICchip used in the present invention is integrated, a substrate containingan epoxy resin, a BT resin, a phenol resin or the like impregnated witha reinforcement or a core material such as a glass epoxy resin, or asubstrate in which prepregs impregnated with an epoxy resin are built upis used. Normally, a substrate used for a printed circuit board isavailable. Alternatively, a two-sided copper-clad laminated board, aone-side board, a resin board without a metallic film or a resin filmcan be used. However, if applied with heat at a temperature of 350° C.or higher, the resin is dissolved and carbonated.

Physical deposition such as deposition or sputtering is conducted to theentire surface of the IC chip to thereby form a conductive metallic filmon the entire surface. The metallic film is preferably formed of one ormore layers of metal such as tin, chromium, titanium, nickel, zinc,cobalt, gold or copper. The thickness thereof is preferably in the rangeof 0.001 to 2.0 μm, more preferably in the range of 0.01 to 1.0 μm.

It is also possible to further provide a metallic film on the metallicfilm by electroless plating or the like. The upper metallic film ispreferably formed out of one or more layers of metal such as nickel,copper, gold or silver. The thickness thereof is preferably 0.01 to 5.0μm, more preferably 0.1 to 3.0 μm.

The metallic film is plated by electroless plating or electroplating.The types of plating materials include nickel, copper, gold, silver,zinc, iron and the like. In view of electrical characteristics,inexpensiveness and the fact that buildup conductor layers formed inlater steps mainly comprise, copper is preferably used. The thickness ofthe plated film is preferably in the range of 1 to 20 μm. If thethickness exceeds that range, undercut sometimes occurs during etchingto thereby generate gaps among the transition layers and via holes to beformed, and interfaces. Thereafter, an etching resist is formed,exposure and development are conducted and the metal other than thetransition layers are exposed and etching is conducted, thereby forminga transition layer on each pad of the IC chip.

Further, instead of the above-stated transition layer manufacturingmethod, it is also possible that a dry film resist is formed on ametallic film formed on the IC chip and the core substrate, a portioncorresponding to the transition layer is removed, a thickening layer isprovided by electroplating, the resist is peeled and that a transitionlayer is formed on each pad of the IC chip by an etching solution.

As a result of devoted studies, the inventor of the present inventiondiscovered that by attaching a heat sink to the rear surface of asemiconductor device embedded in a printed circuit board, heat generatedin the semiconductor device is discharged, warping and breaking do notoccur to the printed circuit board and reliability can be obtained.Here, by forming a buildup wiring out of a resin on the semiconductordevice, it is possible to appropriately connect the semiconductor deviceto the printed circuit board.

It is preferable that the heat sink is connected to the semiconductordevice through a conductive adhesive. This is because the conductiveadhesive is high in heat conductivity and is capable of efficientlydischarging heat generated in the semiconductor device toward the heatsink.

In addition, according to the present invention, prepregs having athrough hole containing therein the IC chip are built up and pressurizedvertically. An epoxy resin is exuded from the prepregs and covers theupper surface of the IC chip. By doing so, the upper surface of the ICchip and that of the core substrate formed by curing the prepregs arecompletely flattened. Due to this, at the time of forming builduplayers, via holes and wirings can be appropriately formed and the wiringreliability of the multilayer printed circuit board can be, therefore,improved.

According to the present invention, a multilayer printed circuit boardprovided with semiconductor devices is manufactured for multiplemultilayer printed circuit boards. The multilayer printed circuit boardis cut into pieces to thereby obtain individual multilayer printedcircuit boards. Due to this, highly reliable multilayer printed circuitboard can be efficiently manufactured.

In addition, according to the present invention, prepregs having athrough hole containing therein the IC chip are built up and pressurizedvertically. An epoxy resin is exuded from the prepregs and covers theupper surface of the IC chip. By doing so, the upper surface of the ICchip and that of the core substrate formed by curing a resin such asprepregs are completely flattened. Due to this, at the time of formingbuildup layers, via holes and wirings can be appropriately formed andthe wiring reliability of the multilayer printed circuit board can be,therefore, improved.

Furthermore, according to a preferred mode of the present invention, aheat sink is attached to the rear surface of a semiconductor deviceembedded into a printed circuit board. By doing so, it is possible todischarge heat generated into the semiconductor device, to prevent theoccurrence of warping and breaking of the printed circuit board and toimprove reliability.

A method of manufacturing a multilayer printed circuit board accordingto one aspect of the present invention is characterized by comprising atleast the following steps (a) to (f):

(a) attaching a sheet to a bottom of a through hole formed in a coresubstrate;

(b) mounting a semiconductor device on said sheet at the bottom of saidthrough hole so that a terminal contacts with said sheet;

(c) filling a resin into said through hole;

(d) pressurizing and curing said resin;

(e) peeling of said sheet; and

(f) forming a buildup layer on an upper surface of said semiconductordevice.

The semiconductor device is mounted on the sheet at the bottom of thethrough hole of the core substrate so that the terminal contacts withthe sheet, the resin is filled into the through hole and then the sheetis peeled, thereby forming a buildup layer. That is to say, aftermounting the semiconductor device on the sheet so that the terminalthereof contacts with the sheet and peeling the sheet, the buildup layeris formed on the semiconductor device. Due to this, it is possible toappropriately, electrically connect the terminal to the wiring of thebuildup layer and to, therefore, manufacture a highly reliablemultilayer printed circuit board into which the semiconductor device isintegrated.

A method of manufacturing a multilayer printed circuit board accordingto another aspect of the present invention is characterized bycomprising at least the following steps (a) to (i):

(a) attaching a sheet to a bottom of a through hole formed in a coresubstrate;

(b) mounting said sheet on the bottom of said through hole so that aterminal contacts with said sheet;

(c) filling a resin into said through hole;

(d) pressurizing and temporarily curing said resin;

(e) peeling of said sheet;

(f) polishing a bottom side of said core substrate, and exposing thebottom of said semiconductor device;

(g) actually curing said resin;

(h) attaching a radiating plate to the bottom of said semiconductordevice; and

(i) forming a buildup layer on an upper surface of said semiconductordevice.

The semiconductor device is mounted on the sheet at the bottom of thethrough hole of the core substrate so that the terminal of the devicecontacts with the sheet, the resin is filled into the through hole andthen the sheet is peeled, thereby forming a buildup layer. That is tosay, after mounting the semiconductor device on the sheet so that theterminal thereof contacts with the sheet and peeling the sheet, thebuildup layer is formed on the semiconductor device. Due to this, it ispossible to appropriately, electrically connect the terminal to thewiring of the buildup layer and to, therefore, manufacture a highlyreliable multilayer printed circuit into which the semiconductor deviceis integrated.

Furthermore, since the bottom side of the core substrate is polished toexposure the bottom of the semiconductor device, it is possible toattach a radiating plate to the bottom of the semiconductor device andto, therefore, improve the stability of the operation of thesemiconductor device.

As a sheet closing the through hole of the core substrate, a UV tape theviscosity of which is lowered if being applied with UV is preferable.Since the UV tape is peeled without leaving the adhesive on the terminalof the semiconductor device by applying UV, it is possible toappropriately, electrically connect the terminal to the wiring of thebuildup layer and to, therefore, manufacture a highly reliablemultilayer printed circuit board into which the semiconductor device isintegrated.

It is also preferable to pressurize the resin under reduced pressure. Byreducing the pressure, no bubbles remain between the core substrate andthe resin and in the resin, thereby making it possible to improve thereliability of the multilayer printed circuit board.

It is further preferable to provide a taper on the through hole formedin the core substrate. By providing the taper, no bubbles or groovesremain between the through hole of the core substrate and the resin andthe reliability of the multilayer printed circuit board can be improved.Besides, the smoothness of the core substrate can be ensured.

In yet another aspect of the invention, a multilayer printed circuitboard having interlayer insulating layers and conductor layersrepeatedly formed on a substrate in which a semiconductor device isembedded, contained or stored, via holes formed in said interlayerinsulating layers, and establishing electrical connection through saidvia holes, is characterized in that:

an external connection terminal (BGA/PGA) is formed only in a region insaid substrate other than a region right above the semiconductor device.

The region on the substrate of the multilayer printed circuit boar intowhich region the semiconductor device is integrated and the region onthe substrate into which the semiconductor device is not integrated aredifferentiated from each other. Then, the external connection terminal(BGA/PGA) is provided in the region of the substrate into which regionthe semiconductor device is not integrated.

Peeling or cracking which occurs to the surrounding of the above-statedexternal connection terminal (BGA/PGA) is resulted from the differencein thermal expansion among the semiconductor device, the externalsubstrate, the interlayer insulating layer and the solder resist layer.That is to say, the semiconductor device and the external substrate madeof ceramic are high in the coefficient of thermal expansion and expandedless by thermal expansion. The interlayer insulating layer and thesolder resist layer made of the resin, by contrast, are higher in thecoefficient of thermal expansion than the semiconductor device and theexternal substrate and, therefore, expanded more by the thermalexpansion. Because of this difference in the coefficient of thermalexpansion, a stress is concentrated on the surrounding of the externalconnection terminal (GBA/PGA) or the like and peeling and crackingoccur.

In other words, by providing the external connection terminal (BGA/PGA)in the region on the substrate into which region the semiconductordevice is not integrated, the influence of thermal expansion can bereduced. Therefore, it is possible to prevent peeling and cracking fromoccurring to the surrounding of the external connection terminal(BGA/PGA) or the like. Accordingly, it is possible to prevent thedetachment and positional error of the external connection terminal(BGA/PGA) and to improve electrical connection characteristics andreliability.

Here, the external connection terminal signifies a terminal forconnecting a substrate, on which an IC chip is mounted, to an externalsubstrate or so-called mother board or daughter board. The terminaldescribed herein refers to a BGA, PGA or a solder bump.

Still another aspect of the invention according to the multilayerprinted circuit board of the foregoing aspect of the invention istechnically characterized by forming the transition layer on the padportion of the semiconductor device so as to be connected to the viahole formed in the lowermost interlayer resin insulating layer.

The transition layer is formed to cover the pad of the semiconductordevice. By providing the transition layer made of copper or the like onthe die pad, a solvent can be used and a resin residue on the die padcan be prevented. Further, even if the substrate is immersed in anoxide, an oxidizer or an etching solution in later steps or subjected tovarious annealing steps, the die pad is not discolored or dissolved. Theformation of the oxide film of the die pad is prevented. Thus, it ispossible to improve the connection characteristics between the die padand the via hole and reliability. Also, by interposing the transitionlayer having a diameter larger than 20 microns on the die pad of the ICchip, it is possible to ensure connecting the via hole to the transitionlayer. Preferably, the transition layer has a diameter equal to orlarger than the diameter of the via hole.

In still, another aspect of the invention a multilayer printed circuitboard of the foregoing aspect of the invention is characterized in that:

a resin filling material is filled between a recess or a through hole ofsaid substrate into which the semiconductor device is embedded, storedor contained, and said semiconductor device.

By filling the resin filling material between the recess or the throughhole of the substrate and the semiconductor device, the adhesion betweenthe substrate and the semiconductor device can be improved. In addition,to relax a stress generated by thermal expansion, this resin fillingmaterial can prevent the cracking of the core substrate and the wavinessof the interlayer resin insulating layer and the solder resist layer.Due to this, it is possible to prevent peeling and cracking fromoccurring to the surrounding of the solder bump or the like.Accordingly, it is possible to prevent the detachment and positionalerror of the solder bump and to, therefore, improve electricalconnection characteristics and reliability. As the resin fillingmaterial, a thermosetting resin, a thermoplastic resin or a mixturethereof can be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(A), 1(B) and 1(C) are manufacturing step view of a semiconductordevice according to the first embodiment of the present invention;

FIGS. 2(A), 2(B) and 2(C) are manufacturing step views of thesemiconductor device according to the first embodiment of the presentinvention;

FIGS. 3(A) and 3(B) are manufacturing step views of the semiconductordevice according to the first embodiment of the present invention;

FIG. 4(A) is a plan view of a silicon wafer 20A according to the firstembodiment, and FIG. 4(B) is a plan view of the semiconductor devicedivided into pieces;

FIGS. 5(A)-5(D) are manufacturing step views of a semiconductor deviceaccording to the first modification of the first embodiment;

FIGS. 6(A), 6(B) and 6(C) are manufacturing step views of thesemiconductor device according to the first modification of the firstembodiment;

FIGS. 7(A) and 7(B) are manufacturing step views of the semiconductordevice according to the first modification of the first embodiment;

FIGS. 8(A), 8(B), 8(C) and 8(D) are manufacturing step views of asemiconductor device according to the second modification of the firstembodiment;

FIGS. 9(A), 9(B), 9(C) and 9(D) are manufacturing step views of thesemiconductor device according to the first modification of the firstembodiment;

FIGS. 10(A), 10(B), 10(C) and 10(D) are manufacturing step views of amultilayer printed circuit board according to the first embodiment;

FIGS. 11(A), 11(B) and 11(C) are manufacturing step views of themultilayer printed circuit board according to the first embodiment;

FIGS. 12(A), 12(B) and 12(C) are manufacturing step views of themultilayer printed circuit board according to the first embodiment;

FIGS. 13(A), 13(B) and 13(C) are manufacturing step views of themultilayer printed circuit board according to the first embodiment;

FIG. 14 is a cross-sectional view of the multilayer printed circuitboard according to the first embodiment;

FIGS. 15(A), 15(B), 15(C) and 15(D) are manufacturing step views of amultilayer printed circuit board according to the first modification ofthe first embodiment;

FIG. 16 is a cross-sectional view of the multilayer printed circuitboard according to the first modification of the first embodiment;

FIG. 17 is a table showing the results of estimating the semiconductordevices of the first embodiment and the first modifications of the firstembodiment;

FIG. 18 is a table showing the results of estimating the semiconductordevices of the second modifications and the third modifications withrespect to comparison examples;

FIGS. 19(A), 19(B) and 19(C) are manufacturing step views of amultilayer printed circuit board according to the second embodiment ofthe present invention;

FIGS. 20(A), 20(B) and 20(C) are manufacturing step views of themultilayer printed circuit board according to the second embodiment;

FIGS. 21(A), 21(B) and 21(C) are manufacturing step views of themultilayer printed circuit board according to the second embodiment;

FIGS. 22(A), 22(B) and 22(C) are manufacturing step views of themultilayer printed circuit board according to the second embodiment;

FIGS. 23(A), 23(B) and 23(C) are manufacturing step views of themultilayer printed circuit board according to the second embodiment;

FIG. 24 is a cross-sectional view of the multilayer printed circuitboard according to the second embodiment;

FIGS. 25(A), 25(B), 25(C) and 25(D) are manufacturing step views of amultilayer printed circuit board according to the first modification ofthe second embodiment;

FIG. 26 is a cross-sectional view of the multilayer printed circuitboard according to the first modification of the second embodiment;

FIGS. 27(A), 27(B) and 27(C) are manufacturing step views of amultilayer printed circuit board according to the second modification ofthe second embodiment;

FIGS. 28(A), 28(B) and 28(C) are manufacturing step views of amultilayer printed circuit board according to the third embodiment ofthe present invention;

FIGS. 29(A), 29(B) and 29(C) are manufacturing step views of themultilayer printed circuit board according to the third embodiment;

FIGS. 30(A), 30(B) and 30(C) are manufacturing step views of themultilayer printed circuit board according to the third embodiment;

FIGS. 31(A), 31(B) and 31(C) are manufacturing step views of themultilayer printed circuit board according to the third embodiment;

FIGS. 32(A), 32(B) and 32(C) are manufacturing step views of themultilayer printed circuit board according to the third embodiment;

FIG. 33 is a cross-sectional view of the multilayer printed circuitboard according to the third embodiment;

FIGS. 34(A), 34(B), 34(C) and 34(D) are manufacturing step views of amultilayer printed circuit board according to the first modification ofthe third embodiment;

FIG. 35 is across-sectional view of the multilayer printed circuit boardaccording to the first modification of the third embodiment;

FIGS. 36(A), 36(B) and 36(C) are manufacturing step views of themultilayer printed circuit board according to the first modification ofthe third embodiment;

FIGS. 37(A), 37(B) and 37(C) are manufacturing step views of themultilayer printed circuit board according to the first modification ofthe third embodiment;

FIGS. 38(A), 38(B) and 38(C) are manufacturing step views of themultilayer printed circuit board according to the first modification ofthe third embodiment;

FIGS. 39(A), 39(B) and 39(C) are manufacturing step views of themultilayer printed circuit board according to the first modification ofthe third embodiment;

FIGS. 40(A), 40(B) and 40(C) are manufacturing step views of themultilayer printed circuit board according to the first modification ofthe third embodiment;

FIG. 41 is a cross-sectional view of the multilayer printed circuitboard according to the first modification of the third embodiment;

FIGS. 42(A), 42(B), 42(C) and 42(D) are manufacturing step views of amultilayer printed circuit board according to the first other example ofthe first modification;

FIG. 43 is a cross-sectional view of a multilayer printed circuit boardaccording to the first other example of the first modification;

FIGS. 44(A), 44(B) and 44(C) are manufacturing step views of amultilayer printed circuit board according to the second other exampleof the first modification of the third embodiment;

FIGS. 45(A), 45(B), 45(C), 45(D) and 45(E) are manufacturing step viewsof a multilayer printed circuit board according to the secondmodification of the third embodiment;

FIGS. 46(A), 46(B), 46(C) and 46(D) are manufacturing step views of themultilayer printed circuit board according to the second modification ofthe third embodiment;

FIGS. 47(A), 47(B) and 47(C) are manufacturing step views of themultilayer printed circuit board according to the second modification ofthe third embodiment;

FIGS. 48(A), 48(B) and 48(C) are manufacturing step views of themultilayer printed circuit board according to the second modification ofthe third embodiment;

FIGS. 49(A), 49(B) and 49(C) are manufacturing step views of themultilayer printed circuit board according to the second modification ofthe third embodiment;

FIG. 50 is a cross-sectional view of the second modification of thethird embodiment;

FIGS. 51(A), 51(B), 51(C) and 51(D) are manufacturing step views of amultilayer printed circuit board according to the first other example ofthe second modification of the third embodiment;

FIG. 52 is across-sectional view of the multilayer printed circuit boardaccording to the first other example of the second modification;

FIGS. 53(A), 53(B), 53(C), 53(D) and 53(E) are manufacturing step viewsof a multilayer printed circuit board according to the fourth embodimentof the present invention;

FIGS. 54(A), 54(B), 54(C), 54(D) and 54(E) are manufacturing step viewsof the multilayer printed circuit board according to the fourthembodiment;

FIGS. 55(A), 55(B), 55(C) and 55(D) are manufacturing step views of themultilayer printed circuit board according to the fourth embodiment;

FIGS. 56(A), 56(B) and 56(C) are manufacturing step views of themultilayer printed circuit board according to the fourth embodiment;

FIG. 57 is a cross-sectional view of the multilayer printed circuitboard according to the fourth embodiment;

FIGS. 58(A), 58(B), 58(C) and 58(D) are manufacturing step views of amultilayer printed circuit board according to the fifth embodiment ofthe present invention;

FIGS. 59(A), 59(B) and 59(C) are manufacturing step views of themultilayer printed circuit board according to the fifth embodiment;

FIGS. 60(A), 60(B) and 60(C) are manufacturing step views of themultilayer printed circuit board according to the fifth embodiment;

FIGS. 61(A), 61(B) and 61(C) are manufacturing step views of themultilayer printed circuit board according to the fifth embodiment;

FIGS. 62(A) and 62(B) are manufacturing step views of the multilayerprinted circuit board according to the fifth embodiment;

FIG. 63 is across-sectional view of the multilayer printed circuit boardaccording to the fifth embodiment;

FIG. 64 is across-sectional view of the multilayer printed circuit boardaccording to the fifth embodiment;

FIG. 65 is a cross-sectional view taken along line E-E of FIG. 63;

FIG. 66(A) is a plan view of the multilayer printed circuit boardaccording to the fifth embodiment, FIG. 66(B) is a plan view of themultilayer printed circuit board on which bumps are arranged in astaggered manner and FIG. 66(C) is a plan view of a multilayer printedcircuit board according to a comparison;

FIGS. 67(A), 67(B) and 67(C) are manufacturing step views of amultilayer printed circuit board according to another example of thefifth embodiment;

FIGS. 68(A), 68(B) and 68(C) are manufacturing step views of amultilayer printed circuit board according to first modification of thefifth embodiment of the present invention;

FIGS. 69(A), 69(B) and 69(C) are manufacturing step views of themultilayer printed circuit board according to first modification of thefifth embodiment; and

FIGS. 70(A), 70(B) and 70(C) are manufacturing step views of themultilayer printed circuit board according to first modification of thefifth embodiment.

BEST MODES FOR WORKING THE INVENTION

The embodiments of the present invention will be described hereinafterwith reference to the drawings.

A. Semiconductor Device

First, the constitution of a semiconductor device (or an IC chip)according to the first embodiment of the present invention will bedescribed with reference to FIG. 3(A) which is a cross-sectional view ofa semiconductor device 20 and to FIG. 4(B) which is a plan view thereof.

First Embodiment

As shown in FIG. 3(B), die pads 22 and wirings (not shown) are arrangedon the upper surface of the semiconductor device 20, a protective film24 is applied on the respective die pads 22 and wirings and the openingsof the protective film 24 are formed on the respective die pads 22.Transition layers 38 mainly comprising copper are formed on therespective die pads 22. Each transition layer 38 comprises a thin filmlayer 33 and a thickening layer 37. In other words, the transition layer38 is formed out of metallic films of two or more layers.

Next, the method of manufacturing the semiconductor device stated abovewith reference to FIG. 3(B) will be described with reference to FIGS. 1to 4.

(1) First, wirings 21 and die pads 22 are formed on a silicon wafer 20Ashown in FIG. 1(A) in an established manner (see FIG. 1(B) and FIG. 4(A)which is a plan view of FIG. 1(B), it is noted that FIG. 1(B) is across-sectional view taken along B-B of FIG. 4(A)).(2) Next, a protective film 24 is formed on the respective die pads 22and wirings 21 and openings 24 a are formed on the respective die pads22 (see FIG. 1(C)).(3) Physical deposition such as deposition or sputtering is conducted tothe silicon wafer 20A, thereby forming a conductive metallic film (or athin film layer) 33 on the entire surface of the silicon wafer 20A (seeFIG. 2(A)). It is preferable that the thickness of the conductivemetallic film is in the range of 0.001 to 2.0 μm. If the thickness isbelow that range, the thin film layer cannot be formed on the entiresurface. If the thickness exceeds that range, the thickness of theformed film becomes irregular. The optimum range is between 0.01 and 1.0μm. Metal for use in the formation of the metallic film is preferablyselected from a group comprising tin, chromium, titanium, nickel, zinc,cobalt, gold and copper. The metal serves as the protective film of thedie pads and the electrical characteristics of the metal does notdeteriorate. In the first embodiment, the thin film layer 33 is formedout of chromium by sputtering. Chromium is good in adhesiveness to metaland is capable of suppressing the entry of moisture. It is also possibleto provide copper on the chromium layer by sputtering. Alternatively,two layers of chromium and copper can be formed continuously in a vacuumchamber. At this moment, the thickness of the chromium layer is about0.05 to 0.1 μm and that of the copper layer is about 0.5 μm.(4) Then, a resist layer made of a liquid resist, a photosensitiveresist or a dry film is formed on the thin film 33. A mask (not shown)on which portions on which transition films 38 are formed are drawn isput on the resist layer, exposure and development are conducted andportions 35 a on which the resist 35 is not formed are thereby formed.Electroless plating is conducted to thereby provide thickening layers(or electroplated films) 37 on the respective resist layer unformedportions 35 a (see FIG. 2(B)). Types of plating materials includecopper, nickel, gold, silver, zinc, iron and the like. In view ofelectrical characteristics, inexpensiveness and the fact that aconductor layer to be built up in a later step mainly comprise copper,copper is preferable. In the first embodiment, copper is used. Thethickness of each thickening layer 37 is preferably in the range of 1 to20 μm.(5) After removing the plating resist 35 with an alkaline solution orthe like, the metallic film 33 under the plating resist 35 is removedwith an etching solution of sulfuric acid-oxygenated water, ferricchloride, cupric chloride, cupric complex-organic acid salt or the like,thereby forming transition layers 38 on the respective pads 22 of the ICchip (see FIG. 2(C)).(6) Next, an etching solution is sprayed on the substrate and thesurfaces of the transition layers 38 are etched, thereby forming roughsurfaces 38α (see FIG. 3(A)). The rough surfaces 38α can be formed byconducting electroless plating or an oxidization-reduction process.(7) Finally, the silicon wafer 20A on which the transition layers 38 areformed are divided into pieces by dicing or the like and semiconductordevices 20 are formed (see FIG. 3(B) and FIG. 4(B) which is a plan viewof FIG. 3(B)). Thereafter, an operation verification test and/or anelectrical test may be conducted to the divided semiconductor devices 20at need. Since the transition layers 38 larger than the die pads 22 areformed on each semiconductor device 20, a probe pin can be easilycontacted with the semiconductor device 20 and test accuracy is high.

First Other Example of First Embodiment

In the above-stated first embodiment, the thin film layer 33 is formedout of chromium. In the first other example, by contrast, the thin filmlayer 33 is formed out of titanium. Titanium is provided by depositionor sputtering. Since titanium has good adhesiveness to metal, it ispossible to suppress the entry of moisture.

Second Other Example of First Embodiment

In the above-stated first embodiment, the thin film layer 33 is formedout of chromium. In the second other example, by contrast, a thin filmlayer 33 is formed out of tin. Since tin has good adhesiveness to metal,it is possible to suppress the entry of moisture.

Third Other Example of First Embodiment

In the above-stated first embodiment, a thin film layer 33 is formed outof chromium. In the third other example, by contrast, the thin filmlayer 33 is formed out of zinc.

Fourth Other Example of First Embodiment

In the above-stated first embodiment, a thin film layer 33 is formed outof chromium. In the fourth other example, by contrast, the thin filmlayer 33 is formed out of nickel. Nickel is provided by sputtering.Since nickel has good adhesiveness to metal, it is possible to suppressthe entry of moisture.

Fifth Other Example of First Embodiment

In the above-stated first embodiment, a thin film layer 33 is formed outof chromium. In the fifth other example, by contrast, the thin filmlayer 33 is formed out of cobalt.

In each of the above other examples, copper may be further built up onthe thin film layer.

First Modification of First Embodiment

A semiconductor device 20 according to the first modification of thefirst embodiment will be described with reference to FIG. 7(B). In caseof the semiconductor device according to the first embodiment statedabove with reference to FIG. 3(B), each of the transition layers 38 hasa two-layer structure comprising the thin film layer 33 and thethickening layer 37. In the first modification, by contrast, eachtransition layer 38 is constituted to have a three-layer structurecomprising the first thin film layer 33, the second thin film layer 36and a thickening layer 37 as shown in FIG. 7(B).

Next, the method of manufacturing the semiconductor device according tothe first modification described above with reference to FIG. 7(B) willbe described with reference to FIGS. 5 to 7.

(1) First, wirings 21 and die pads 22 are formed on a silicon wafer 20Ashown in FIG. 5(A) (see FIG. 5(B)).

(2) Next, a protective film 24 is formed on the wirings 21 and the diepads 22 (see FIG. 5(C)).

(3) Physical deposition such as deposition or sputtering is conducted tothe silicon wafer 20A, thereby forming a conductive metallic film (orthe first thin film layer) 33 on the entire surface of the silicon wafer20A (see FIG. 5(D)). The thickness of the metallic film is preferably inthe range of 0.001 to 2.0 μm. If the thickness is below that range, thethin film layer cannot be formed. If the thickness exceeds that range,the thickness of the formed film becomes irregular. The optimum range isbetween 0.01 to 1.0 μm. Metal for use in the formation of the metallicfilm is preferably selected from a group comprising tin, chromium,titanium, nickel, zinc, cobalt, gold and copper. The metal serves as theprotective film of the die pads and the electrical characteristics ofthe metal does not deteriorate. Since chromium, nickel and titanium havegood adhesiveness to metal, they can suppress the entry of moisture. Inthe first modification, the first thin film layer 33 is formed out ofchromium.(4) The second thin film layer 36 is built up on the first thin filmlayer 33 by any one of sputtering, deposition and electroless platingmethods (see FIG. 6(A)). Metal to be built up is preferably selectedfrom a group comprising nickel, copper, gold and silver. It is morepreferable to form the second thin film layer 36 out of copper ornickel. The reason is as follows. Copper is inexpensive and good inelectrical conductivity. Nickel is good in adhesiveness to a thin filmand hardly peeled or cracked. The thickness of the second thin filmlayer 36 is preferably 0.01 to 5.0 μm and more preferably 0.1 to 3.0 μm.In the first modification, the second thin film layer 36 is formed byelectroless copper plating.

The preferable combinations of the first and second thin film layers arechromium-copper layers, chromium-nickel layers, titanium-copper layers,titanium-nickel layers and the like. These combinations are superior tothe other combinations in coupling characteristics with respect to metaland electrical conductivity.

(5) Thereafter, a resist layer is formed on the second thin film layer36. A mask (not shown) is put on the resist layer, exposure anddevelopment are conducted and portions 35 a on which the resist 35 isnot formed are formed. Thickening layers (or electroless plated layers)37 are provided on the resist unformed sections 35 a by electroplating(see FIG. 6(B)). Types of plating materials used in the formation ofplated layers include copper, nickel, gold, silver, zinc, iron and thelike. In view of electrical characteristics, inexpensiveness and thefact that a conductor layer to be built up in a later step mainlycomprises copper, copper is preferable. In the first modification,therefore, copper is used. The thickness of each thickening layer 37 ispreferably in the range of 1 to 20 μm.(6) After removing the plating resist 35 with an alkaline solution orthe like, the second thin film layer 36 and the metallic film 33 underthe plating resist 35 are removed with an etching solution of sulfuricacid-oxygenated water, ferric chloride, cupric chloride, cupriccomplex-organic acid salt or the like, thereby forming transition layers38 on the respective pads 22 of the IC chip (see FIG. 6(C)).(7) Next, an etching solution is sprayed on the substrate and thesurfaces of the transition layers 38 are etched, thereby forming roughsurfaces 38 a (see FIG. 7(A)). The rough surfaces 38 a can be formed byconducting electroless plating or an oxidization-reduction process.(8) Finally, the silicon wafer 20A on which the transition layers 38 areformed are divided into pieces by dicing or the like and semiconductordevices are formed (see FIG. 7(B)).

First Other Example of First Modification of First Embodiment

In the first modification stated above, the first thin layer 33 isformed out of chromium, the second thin film layer 36 is formed byelectroless copper plating and the thickening layer 37 is formed bycopper electroplating. In the first other example, by contrast, thefirst thin film layer 33 is formed out of chromium, the second thin filmlayer 36 is formed by sputtering copper and the thickening layer 37 isformed by copper electroplating. The thickness of the chromium layer is0.07 μm, that of the copper layer is 0.5 μm and that of theelectroplated copper layer is 15 μm.

Second Other Example of First Modification of First Embodiment

In the second other example, the first thin film layer 33 is formed outof titanium, the second thin film layer 36 is formed by electrolesscopper plating and the thickening layer 37 is formed by copperelectroplating. The thickness of the titanium layer is 0.07 μm, that ofthe copper plated layer is 1.0 μm and that of the copper electroplatedlayer is 17 μm.

Third Other Example of First Modification of First Embodiment

In the third other example, the first thin film layer 33 is formed outof titanium, the second thin film layer 36 is formed by sputteringcopper and the thickening layer 37 is formed by copper electroplating.The thickness of the titanium layer is 0.06 μm, that of the copper layeris 0.5 μm and that of the copper electroplated layer is 15 μm.

Fourth Other Example of First Modification of First Embodiment

In the fourth other example, the first thin film layer 33 is formed outof chromium, the second thin film layer 36 is formed by electrolessnickel plating and the thickening layer 37 is formed by copperelectroplating. The thickness of the chromium layer is 0.07 μm, that ofthe copper plated layer is 1.0 μm and the copper electroplated layer is15 μm.

Fifth Other Example of First Modification of First Embodiment

In the fifth example, the thin film layer 33 is formed out of titanium,the second thin film layer 36 is formed by electroless nickel platingand the thickening layer 37 is formed by copper electroplating. Thethickness of the titanium layer is 0.05 μm, that of the nickel platedlayer is 1.2 μm and that of the copper electroplated layer is 15 μm.

Second Modification of First Embodiment

The method of manufacturing a semiconductor device 20 according to thesecond modification will be described with reference to FIG. 8. Theconstitution of the semiconductor device in the second modification isalmost the same as that in the first embodiment stated above withreference to FIG. 3(B). In the first embodiment, a semi-additive step isemployed and the thickening layers 37 are formed on the respectiveresist unformed portions, thereby forming the transition layers 38. Inthe second modification, by contrast, an additive step is employed andthickening layers 37 are uniformly formed. Thereafter, a resist isprovided and resist unformed portions are etched away, thereby formingtransition layers 38.

The manufacturing method in the second modification will be describedwith reference to FIG. 8.

(1) As described above in the first embodiment with reference to FIG.2(B), physical deposition such as deposition or sputtering is conductedto a silicon wafer 20A, thereby forming a conductive metallic film 33 onthe entire surface of the silicon wafer 20A (see FIG. 8(A)). Thethickness of the conductive metallic film 33 is preferably in the rangeof 0.001 to 2.0 μm. If the thickness is below that range, a thin filmlayer cannot be formed on the entire surface. If the thickness exceedsthat range, the thickness of the film to be formed becomes irregular.The optimum range is preferably 0.01 to 1.0 μm. Metal for use in theformation of the metallic film 33 is preferably selected from a groupcomprising tin, chromium, titanium, nickel, zinc, cobalt, gold andcopper. The metal serves as the protective film of die pads and theelectrical characteristics of the metal does not deteriorate. In thesecond modification, the thin film layer 33 is formed by sputteringchromium. The thickness of the chromium thin film layer 33 is 0.05 μm.(2) Electroplating is conducted to provide a thickening layer (or anelectroplated film) 37 on the thin film layer 33 (see FIG. 8(B)). Typesof plating materials include copper, nickel, gold, silver, zinc, ironand the like. In view of electrical characteristics, inexpensiveness andthe fact that a conductor layer to be built up in a later step mainlycomprises copper, copper is preferable. In the second modification,therefore, copper is used. The thickness of the thickening layer 37 ispreferably in the range of 1.0 to 20 μm. If the thickness exceeds thatrange, undercut may possibly occur during etching to be described laterto thereby generate gaps in the interfaces between a transition layerand via holes to be formed.(3) Thereafter, a resist layer 35 is formed on the thickening layer 37(see FIG. 8(C)).(4) The metallic film 33 and the thickening layer 37 on the portions onwhich the resist 35 is not formed are etched away with an etchingsolution of sulfuric acid-oxygenated water, ferric chloride, cupricchloride, cupric complex-organic acid salt or the like, thereby formingtransition layers 38 on the respective pads 22 of the IC chip (see FIG.8(D)). Since following steps are the same as those in the firstembodiment, no description will be given thereto.

First Other Example of Second Modification of First Embodiment

In the second modification stated above, the thin film layer 33 isformed out of chromium. In the first other example, by contrast, a thinfilm layer 33 is formed out of titanium.

Third Modification of First Embodiment

The method of manufacturing a semiconductor device 20 according to thethird modification will be described with reference to FIG. 9. In caseof the semiconductor device according to the second modification statedabove with reference to FIG. 8, each transition layer 38 has a two-layerstructure comprising the thin film layer 33 and the thickening layer 37.In the third modification, as shown FIG. 9 (D), by contrast, atransition layer 38 is constituted to have a three-layer structurecomprising the first thin film layer 33, the second thin film layer 36and a thickening layer 37.

The manufacturing method in the third modification will be describedwith reference to FIG. 9.

(1) As in the case of the first modification in the first embodimentstated above with reference to FIG. 6(A), the second thin film layer 36is built up on the first thin film layer 33 by sputtering, deposition orelectroless plating (see FIG. 9(A)). Metal to be built up in this caseis preferably selected from a group comprising nickel, copper, gold andsilver. Copper or nickel is more preferable. The reason is as follows.Copper is inexpensive and good in electrical conductivity. Nickel isgood in adhesiveness to a thin film and is hardly peeled or cracked. Inthe third modification, the second thin film layer 36 is formed byelectroless copper plating. The thickness of the second thin film layer36 is preferably 0.01 to 5.0 μm and more preferably 0.1 to 3.0 μm.

The preferable combinations of the first thin film layer and the secondthin film layer are chromium-copper layers, chromium-nickel layers,titanium-copper layers, titanium-nickel layers. These combinations aresuperior to the other combinations in coupling characteristics withrespect to metal and electrical conductivity.

(2) Electroplating is conducted, thereby uniformly providing athickening layer 37 made of nickel, copper, gold, silver, zinc or ironon the second thin film layer 36 (see FIG. 9(B)). The thickness of thethickening layer 37 is preferably 1 to 20 μm.

(3) Thereafter, a resist layer 35 is formed on the thickening layer 37(see FIG. 9(C)).

(4) The first thin film layer 33, the second thin film layer 36 and thethickening layer 37 on portions on which the resist 35 is not formed areremoved with an etching solution of sulfuric acid-oxygenated water,ferric chloride, cupric chloride, cupric complex-organic acid salt orthe like and the resist 35 is peeled, thereby forming transition layers38 on the respective pads 22 of the IC chip (see FIG. 9(D)). Sincefollowing steps are the same as those in the first embodiment, nodescription will be given thereto.

First Other Example of Third Modification of First Embodiment

In the third modification stated above, the first thin film layer 33 isformed out of chromium, the second thin film layer 36 is formed byelectroless copper plating and the thickening layer 37 is formed bycopper electroplating. In the first other example, by contrast, thefirst thin film layer 33 is formed out of chromium, the second thin filmlayer 36 is formed by sputtering copper and a thickening layer 37 isformed by copper electroplating. The thickness of the chromium layer is0.07 μm, that of the copper layer is 0.5 μm and that of the copperelectroplated layer is 15 μm.

Second Other Example of Third Modification of First Embodiment

In the second other example, the first thin film layer 33 is formed outof titanium, the second thin film layer 36 is formed by electrolesscopper plating and a thickening layer 37 is formed by copperelectroplating. The thickness of the titanium layer is 0.07 μm, that ofthe copper layer is 1.0 μm and that of the copper electroplated layer is15 μm.

Third Other Example of Third Modification of First Embodiment

In the third other example, the first thin film layer 33 is formed outof titanium, the second thin film layer 36 is formed by sputteringcopper and the thickening layer 37 is formed by copper electroplating.The thickness of the titanium layer is 0.07 μm, that of the copper layeris 0.5 μm and that of the copper electroplated layer is 18 μm.

Fourth Other Example of Third Modification of First Embodiment

In the fourth other example, the first thin film layer 33 is formed outof chromium, the second thin film layer 36 is formed by electrolessnickel plating and a thickening layer 37 is formed by copperelectroplating. The thickness of the chromium layer is 0.06 μm, that ofthe nickel layer is 1.2 μm and that of the copper electroplated layer is16 μm.

Fifth Other Example of Third Modification of First Embodiment

In the fifth other example, the first thin film layer 33 is formed outof titanium, the second thin film layer 36 is formed by electrolessnickel plating and a thickening layer 37 is formed by copperelectroplating. The thickness of the titanium layer is 0.07 μm, that ofthe nickel layer is 1.1 μm and that of the copper electroplated layer is15 μm.

B. Multilayer Printed Circuit Board into which Semiconductor Device isIntegrated.

Next, description will be given to the constitution of a multilayerprinted circuit board provided by embedding and containing asemiconductor device (or an IC chip) 20 in the above-stated first tothird modifications into the recess, gap or opening of a core substrate.

First Embodiment

As shown in FIG. 14, the multilayer printed circuit board 10 comprises acore substrate 30 containing therein an IC chip 20, an interlayer resininsulating layer 50 and an interlayer resin insulating layer 150. Viaholes 60 and conductor circuits 58 are formed on the interlayer resininsulating layer 50. Via holes 160 and conductor circuits 158 are formedon the interlayer resin insulating layer 150.

A solder resist layer 70 is provided on the interlayer resin insulatinglayer 150. Solder bumps 76 for connecting to an external substrate suchas a daughter board or a mother board, which is not shown in FIG. 14,are provided on the conductor circuits 158 under the openings 71 of thesolder resist layer 70, respectively.

In the multilayer printed circuit board 10 in this embodiment, the ICchip 20 is integrated into the core substrate 30 and transition layers38 are provided on the respective pads 22 of the IC chip 20. Due tothis, it is possible to electrically connect the IC chip to themultilayer printed circuit board (or package substrate) without usinglead members and a sealing resin. Further, since the transition layers38 are formed on the IC chip portion, the IC chip portion is flattenedand the upper interlayer insulating layer 50 is, therefore, flattened tothereby provide uniform film thickness. Further, because of thetransition layers, it is possible to maintain the stability of shapeeven if the via holes 60 provided in the upper layer are formed.

Furthermore, by providing the transition layers 38 made of copper on therespective die pads 22, it is possible to prevent resin residues on thedie pads 22 and to prevent the die pads 22 from being discolored ordissolved even after impregnating the multilayer printed circuit boardin an acid, an oxidizer or an etching solution in a later step orconducting various annealing steps. Thus, connection characteristicbetween the die pads of the IC chip and the via holes and reliabilitycan be improved. Besides, by interposing the transition layers 38 eachhaving a diameter of 60 μm or more on the respective pads 22 each havinga diameter of 40 μm, it is possible to ensure connecting the via holeseach having a diameter of 60 μm.

Next, the method of manufacturing the multilayer printed circuit boarddescribed above with reference to FIG. 14 will be described withreference to FIGS. 10 to 13.

(1) First, an insulating resin substrate (or a core substrate) 30 inwhich prepregs each having a core material made of glass cloths or thelike and impregnated with a resin such as epoxy are built up, is used asa starting material (see FIG. 10(A)). Next, a recess 32 for containingan IC chip is formed on one side of the core substrate 30 by counterboring (see FIG. 10(B). While the recess is provided by counter boringherein, it is also possible to form a core substrate having a containingsection by building up an insulating resin substrate having an openingto an insulating resin substrate without an opening.(2) Then, an adhesive material 34 is applied to the recess 32 using aprinting machine. At this time, potting instead of application may beconducted. Next, an IC chip 20 is mounted on the adhesive material 34(see FIG. 10(C)).(3) Then, the upper surface of the IC chip 20 is depressed or struck tothereby completely contain the IC chip 20 in the recess 32 (see FIG.10(D). By doing so, the core substrate 30 can be smoothed. At thismoment, the adhesive material 34 is sometimes applied on the uppersurface of the IC chip 20. However, as described later, since a resinlayer is provided on the upper surface of the IC chip 20 and thenopenings for via holes are provided by laser, the adhesive material 34does not influence the connection between transition layers 38 and viaholes.(4) A thermosetting resin sheet having a thickness of 50 μm isvacuum-compression laminated onto the substrate which has gone throughthe above-stated steps at a pressure of 5 kg/cm² while raisingtemperature to 50 to 150° C., thereby providing an interlayer resininsulating layer 50 (see FIG. 11(A)). The degree of vacuum at the timeof vacuum compression is 10 mmHg.(5) Next, using CO₂ gas laser having a wavelength of 10.4 μm, via holeopenings 48 each having a diameter of 60 μm are provided in theinterlayer resin insulating layer 50 under the conditions of a beamdiameter of 5 mm, a top hat mode, a pulse width of 5.0 microseconds, amask hole diameter of 0.5 mm and one shot (see FIG. 11(B)). Using apermanganic acid at a temperature of 60° C., resin residues in theopenings 48 are removed. By providing a transition layer 38 made ofcopper on each die pad 22, it is possible to prevent resin residues onthe pad 22, thereby improving connection characteristic between the pad22 and a via hole 60 to be described later and improving reliability.Furthermore, by interposing the transition layer 38 having a diameter of60 μm or more on the die pad 22 having a diameter of 40 μm, it ispossible to ensure connecting the via hole opening 48 having a diameterof 60 μm. While the resin residues are removed by using an oxidizer suchas a permanganic acid, a de-smear process can be also conducted usingoxygen plasma or corona process.(6) Next, the resultant substrate is immersed in an oxidizer such as achromic acid or a permanganic acid or the like, thereby providing arough surface 50α on the interlayer resin insulating layer 50 (see FIG.11( c)). The rough surface 50α is preferably formed to have a thicknessin the range of 0.1 to 5 μm. For example, the substrate is immersed in50 g/l of a sodium permanganate solution at a temperature of 60° C. for5 to 25 minutes, thereby providing a rough surface 50α of 2 to 3 μm.Alternatively, by performing a plasma process using SV-4540 manufacturedby ULVAC JAPAN LTD., the rough surface 50α can be formed on the surfaceof interlayer resin insulating layer 50. In that case, argon gas is usedas inactive gas to perform a plasma process for two minutes underconditions of electric power of 200 W, a gas pressure of 0.6 Pa and atemperature of 70° C.(7) A metallic layer 52 is provided on the interlayer resin insulatinglayer 50 on which the rough surface 50α has been formed (see FIG.12(A)). The metallic layer 52 is formed by electroless plating. Bysupplying a catalyst such as a palladium catalyst to the surface layerof the interlayer resin insulating layer 50 in advance and immersing thesubstrate into an electroless plating solution for 5 to 60 minutes, themetallic layer 52 which is a plated film is provided in the range of 0.1to 5 μm. For example, the substrate is immersed in the followingsolution at a solution temperature of 34° C. for 40 minutes:

[Electroless Plating Solution] NiSO₄ 0.003 mol/l tartaric acid 0.200mol/l copper sulfate 0.030 mol/l HCHO 0.050 mol/l NaOH 0.100 mol/lα,α′-bipyridyl 100 mg/l polyethylene glycol (PEG) 0.10 g/l

Alternatively, an Ni/Cu alloy 52 can be formed on the surface of theinterlayer epoxy resin insulating layer 50 by conducting sputtering withan Ni—Cu alloy 52 as a target under conditions of an air pressure of 0.6Pa, a temperature of 80° C., power of 200 W and a duration of fiveminutes using SV-4540 manufactured by ULVAC JAPAN LTD. At this moment,the thickness of the Ni—Cu alloy layer 52 thus formed is 0.2 μm.

(8) A commercially available photosensitive dry film is bonded to thesubstrate 30 which has been subjected to the above process, a photomaskfilm is mounted, exposure is conducted at 100 mj/cm² and then adevelopment process is conducted with 0.8% sodium carbonate, therebyproviding a plating resist 54 having a thickness of 15 μm. Next,electroplating is conducted under the following conditions, therebyforming an electroplated firm (see FIG. 12(B)). An additive in theelectroplating solution is Kapalacid HL manufactured by Atotech Japan.

[Electroplating Solution] sulfuric acid 2.24 mol/l copper sulfate 0.26mol/l additive 19.5 mol/l (Kapalacid HL manufactured by Atotech Japan)

[Electroplating Conditions] current density 1 A/dm² duration 65 minutestemperature 22 ± 2° C.(9) After separating and removing the plating resist with 5% NaOH, themetallic layer 52 under the plating resist is dissolved and removed byetching using a mixture solution of a nitric acid, a sulfuric acid andoxygenated water, conductor circuits 58 each comprising the metalliclayer 52 and the electroplated film 56 and having a thickness of 16 μmand via holes 60 are formed and etched by an etching solution containinga cupric salt complex and an organic acid, thereby forming roughsurfaces 58α and 60α (see FIG. 12(C)).(10) Next, the steps of (4) to (9) stated above are repeated, therebyforming an upper interlayer resin insulating layer 150 and conductorcircuits 158 (including via holes 160) (see FIG. 13(A)).(11) Then, 46.67 parts by weight of oligomer (having a molecular weightof 4000) which is obtained by forming 50% of epoxy groups of 60 parts byweight of a cresol novolac epoxy resin (manufactured by Nippon KayakuCo., Ltd.) dissolved in diethylene glycol dimethyl ether (DMDG) into anacrylic structure and which imparts photosensitive characteristic, 15parts by weight of 80 wt % of a bisphenol A epoxy resin (product name:Epicoat 1001 manufactured by Yuka Shell) dissolved in methylethyl keton,1.6 parts by weight of an imidazole hardening agent (product name:2E4MZ-CN manufactured by Shikoku Chemicals Corp.), 3 parts by weight ofpolyhydric acryl monomer which is a photosensitive monomer (productname: R604 manufactured by Kyoei Chemical), 1.5 parts by weight ofpolyhydric acryl monomer (product name: DPE6A manufactured by KyoeiChemical), and 0.71 parts by weight of a dispersing defoaming agent(product name: S-65 manufactured by Sannopuko) are contained in acontainer, agitated and mixed to adjust mixture compositions. Then, 2.0parts by weight of benzophenone (manufactured by Kanto Chemical) servingas a photoinitiator and 0.2 parts by weight of Michler's ketone(manufactured by Kanto Chemical) serving as a photosensitizer are addedto the mixture compositions, thereby obtaining a solder resistcomposition (or organic resin insulating material) adjusted to have aviscosity of 2.0 Pa·s.

It is noted that the viscosity is measured by using No. 4 rotor of aB-type viscometer (DVL-B manufactured by Tokyo Keiki) when the velocityis 60 rpm and using No. 3 rotor of the same when the velocity is 6 rpm.

(12) Next, the solder resist composition is applied to the substrate 30to have a thickness of 20 μm and a drying process is conducted at 70° C.for 20 minutes and 70° C. for 30 minutes. Then, a photomask film havinga pattern of the solder resist opening portions drawn thereon and athickness of 5 mm is made hermetic contact with the solder resist layer70, exposure is performed with ultraviolet rays with 1000 mj/cm² andthen a development process is performed with a DMTG solution, therebyforming openings 71 each having a diameter of 200 μm (see FIG. 13(B)).Alternatively, a commercially available solder resist may be used.(13) Next, the substrate on which the solder resist layer (or organicresin insulating layer) 70 is formed, is immersed in an electrolessnickel plating solution containing nickel chloride (2.3×10⁻¹ mol/l),sodium hypophosphite (2.8×10⁻¹ mol/l), sodium citrate (1.6×10⁻¹ mol/l)and having pH=4.5 for 20 minutes, and a nickel plated layer 72 having athickness of 5 μm is formed on each opening portion 71. Then, thesubstrate is further immersed in an electroless plating solutioncontaining gold potassium cyanide (7.6×10⁻³ mol/l), ammonia chloride(1.9×10⁻¹ mol/l), sodium citrate (1.2×10⁻¹ mol/l) and sodiumhypophosphite (1.7×10⁻¹ mol/l) under the condition of 80° C. for 7.5minutes and a gold plated layer 74 having a thickness of 0.03 μm isformed on the nickel plated layer 72, thereby forming a solder pad 75 oneach conductor layer 158 (see FIG. 13(C)).(14) Thereafter, a solder paste is printed on the opening portions 71 ofthe solder resist layer 71 and reflow is conducted at 200° C., therebyforming solder bumps 76. As a result, it is possible to obtain amultilayer printed circuit board 10 into which the IC chip 20 isintegrated and which has the solder bumps 76 (see FIG. 14).

As the solder paste, Sn/Pb, Sn/Sb, Sn/Ag, Sn/Ag/Cu or the like may beused. Needless to say, a solder paste of low a radiation ray type may beused.

In the above-stated embodiment, the thermosetting resin sheet is usedfor the interlayer resin insulating layers 50 and 150. The thermosettingresin insulating sheet contains a refractory resin, soluble particles, ahardening agent and other components. The materials will now bedescribed one by one.

The resin used in the manufacturing method of the present invention hasa structure in that particles soluble in acid or an oxidizer(hereinafter, referred to as “soluble particles”) are dispersed in resinwhich is refractory with respect to acid or an oxidizer (hereinafter,referred to as “refractory resin”).

The expressions “refractory” and “soluble” will now be described. Whenmaterials are immersed in solution composed of the same acid or the sameoxidizers for the same time, a material of a type which is dissolved ata relatively high dissolving rate is called a “soluble” material forconvenience. A material of a type which is dissolved at a relativelyslow dissolving rate is called a “refractory material” for convenience.

The soluble particles are exemplified by resin particles which aresoluble in acid or an oxidizer (hereinafter called “soluble resinparticles”), inorganic particles which are soluble in acid or anoxidizer (hereinafter called “inorganic soluble particles”) and metalparticles which are soluble in acid or an oxidizer (hereinafter called“soluble metal particles”). The foregoing soluble particles may beemployed solely or two or more particles may be employed.

The shape of each of the soluble particles is not limited. The shape maybe a spherical shape or a pulverized shape. It is preferable that theparticles have a uniform shape. The reason for this lies in that a roughsurface having uniformly rough pits and projections can be formed.

It is preferable that the mean particle size of the soluble particles is0.1 μm to 10 μm. When the particles have the diameters satisfying theforegoing range, particles having two or more particle sizes may beemployed. That is, soluble particles having a mean particle size of 0.1μm to 0.5 μm and soluble particles having a mean particle size of 1 μmto 3 μmm may be mixed. Thus, a more complicated rough surface can beformed. Moreover, the adhesiveness with the conductor circuit can beimproved. In the present invention, the particle size of the solubleparticles is the length of a longest portion of each of the solubleparticles.

The soluble resin particles may be particles constituted bythermosetting resin or thermoplastic resin. When the particles areimmersed in solution composed of acid or an oxidizer, the particles mustexhibit dissolving rate higher than that of the foregoing refractoryresin.

Specifically, the soluble resin particles are exemplified by particlesconstituted by epoxy resin, phenol resin, polyimide resin, polyphenyleneresin, polyolefin resin polietelslufon or fluorine resin. The foregoingmaterial may be employed solely or two or more materials may be mixed.

The soluble resin particles may be resin particles constituted byrubber. Rubber above is exemplified by polybutadiene rubber, a varietyof denatured polybutadiene rubber, such as denatured epoxy rubber,denatured urethane rubber or denatured (metha) acrylonitrile rubber, and(metha) acrylonitrile butadiene rubber containing a carboxylic group.When the foregoing rubber material is employed, the soluble resinparticles can easily be dissolved in acid or an oxidizer. That is, whenthe soluble resin particles are dissolved with acid, dissolution ispermitted with acid except for strong acid. When the soluble resinparticles are dissolved, dissolution is permitted with permanganatewhich has a relatively weak oxidizing power. When chromic acid isemployed, dissolution is permitted even at a low concentration.Therefore, retention of the acid or the oxidizer on the surface of theresin can be prevented. When a catalyst, such as palladium chloride, issupplied after the rough surface has been formed as described later,inhibition of supply of the catalyst and oxidation of the catalyst canbe prevented.

The inorganic soluble particles are exemplified by particles made of atleast a material selected from a group comprising an aluminum compound,a calcium compound, a potassium compound, a magnesium compound and asilicon compound.

The aluminum compound is exemplified by alumina and aluminum hydroxide.The calcium compound is exemplified by calcium carbonate and calciumhydroxide. The potassium compound is exemplified by potassium carbonate.The magnesium compound is exemplified by magnesia, dolomite and basicmagnesium carbonate. The silicon compound is exemplified by silica andzeolite. The foregoing material may be employed solely or two or morematerials may be mixed.

The soluble metal particles are exemplified by particles constituted byat least one material selected from a group comprising copper, nickel,iron, zinc, lead, gold, silver, aluminum, magnesium, potassium andsilicon. The soluble metal particles may have surfaces coated with resinor the like in order to maintain an insulating characteristic.

When two or more types of the soluble particles are mixed, it ispreferable that the combination of the two types of soluble particles iscombination of resin particles and inorganic particles. Since each ofthe particles has low conductivity, an insulating characteristic withthe resin film can be maintained. Moreover, the thermal expansion caneasily be adjusted with the refractory resin. Thus, occurrence of acrack of the interlayer resin insulating layer constituted by the resinfilm can be prevented. Thus, separation between the interlayer resininsulating layer and the conductor circuit can be prevented.

The refractory resin is not limited when the resin is able to maintainthe shape of the rough surface when the rough surface is formed on theinterlayer resin insulating layer by using acid or oxidizer. Therefractory resin is exemplified by thermosetting resin, thermoplasticresin and their composite material. As an alternative to this, theforegoing photosensitive resin of a type having photosensitivecharacteristic imparted thereto may be employed. When the photosensitiveresin is employed, exposure and development processes of the interlayerresin insulating layers can be performed to form the openings for thevia holes.

In particular, it is preferable that the resin containing thermosettingresin is employed. In the foregoing case, the shape of the rough surfacecan be maintained against plating solution and when a variety of heatingprocesses are performed.

The refractory resin is exemplified by epoxy resin, phenol resin,phenoxy resin, polyimide resin, polyphenylene resin, polyolefin resin,polyetelslufon and fluorine resin. The foregoing material may beemployed solely or two or more types of the materials may be mixed.

It is preferable that epoxy resin having two or more epoxy groups in onemolecule thereof is employed. The reason for this lies in that theforegoing rough surface can be formed. Moreover, excellent heatresistance and the like can be obtained. Thus, concentration of stressonto the metal layer can be prevented even under a heat cycle condition.Thus, occurrence of separation of the metal layer can be prevented.

The epoxy resin is exemplified by cresol novolac epoxy resin,bisphenol-A epoxy resin, bisphenol-F epoxy resin, phenol novolac epoxyresin, alkylphenol novolac epoxy resin, biphenol-F epoxy resin,naphthalene epoxy resin, dicyclopentadiene epoxy resin, an epoxymaterial constituted by a condensation material of phenol and anaromatic aldehyde having a phenol hydroxyl group, triglycidylisocyanurate and alicyclic epoxy resin. The foregoing material may beemployed solely or two or more material may be mixed. Thus, excellentheat resistance can be realized.

It is preferable that the soluble particles in the resin film accordingto the present invention are substantially uniformly dispersed in therefractory resin. The reason for this lies in that a rough surfacehaving uniform pits and projections can be formed. When via holes andthrough holes are formed in the resin film, adhesiveness with the metallayer of the conductor circuit can be maintained. As an alternative tothis, a resin film containing soluble particles in only the surface onwhich the rough surface is formed may be employed. Thus, the portions ofthe resin film except for the surface is not exposed to acid or theoxidizer. Therefore, the insulating characteristic between conductorcircuits through the interlayer resin insulating layer can reliably bemaintained.

It is preferable that the amount of the soluble particles which aredispersed in the refractory resin is 3 wt % to 40 wt % with respect tothe resin film. When the amount of mixture of the soluble particles islower than 3 wt %, the rough surface having required pits andprojections cannot be formed. When the amount is higher than 40 wt %,deep portions of the resin film are undesirably dissolved when thesoluble particles are dissolved by using acid or the oxidizer. Thus, theinsulating characteristic between the conductor circuits through theinterlayer resin insulating layer constituted by the resin film cannotbe maintained. Thus, short circuit is sometimes is caused to occur.

It is preferable that the resin film contains a hardening agent andother components as well as the refractory resin.

The hardening agent is exemplified by an imidazole hardening agent, anamine hardening agent, a guanidine hardening agent, an epoxy adduct ofeach of the foregoing hardening agents, a microcapsule of each of theforegoing hardening agents and an organic phosphine compound, such astriphenylphosphine or tetraphenyl phosphonium tetraphenyl borate.

It is preferable that the content of the hardening agent is 0.05 wt % to10 wt % with respect to the resin film. When the content is lower than0.05 wt %, the resin film cannot sufficiently be hardened. Thus,introduction of acid and the oxidizer into the resin film occursgreatly. In the foregoing case, the insulating characteristic of theresin film sometimes deteriorates. When the content is higher than 10 wt%, an excessively large quantity of the hardening agent componentsometimes denatures the composition of the resin. In the foregoing case,the reliability sometimes deteriorates.

The other components are exemplified by an inorganic compound which doesnot exert an influence on the formation of the rough surface and afiller constituted by resin. The inorganic compound is exemplified bysilica, alumina and dolomite. The resin is exemplified by polyimideresin, polyacrylic resin, polyamideimide resin, polyphenylene resin,melanine resin and olefin resin. When any one of the foregoing fillersis contained, conformity of the thermal expansion coefficients can beestablished. Moreover, heat resistance and chemical resistance can beimproved. As a result, the performance of the multilayer printed circuitboard can be improved.

The resin film may contain solvent. The solvent is exemplified byketone, such as acetone, methylethylketone or cyclohexane; aromatichydrocarbon, such as ethyl acetate, butyl acetate, cellosolve acetate,toluene or xylene. The foregoing material may be employed solely or twoor more materials may be mixed. It is noted, however, interlayer resininsulating layer is resolved and carbonated if heated at a temperatureof 350° C. or higher.

First Modification of First Embodiment

Next, description will be given to a multilayer printed circuit boardaccording to the first modification of the first embodiment withreference to FIG. 16.

In the first embodiment stated above, description has been given to acase where the BGA's are arranged. In the first modification, which isalmost the same as the first embodiment, the multilayer printed circuitboard is constituted in a PGA type for establishing connection throughconductive connection pins 96 as shown in FIG. 16. Also, via holes areformed by laser in the above-stated first embodiment, whereas via holesare formed by photoetching in the first modification.

The method of manufacturing the multilayer printed circuit boardaccording to the first modification will be described with reference toFIG. 15.

(4) As in the case of the first embodiment, a thermosetting epoxy resin50 having a thickness of 50 μm is applied to the substrate which hasgone through the steps (1) to (3) (see FIG. 15(A)).

(5) Next, a photomask film 49 having black circles 49 a corresponding tovia hole formed positions drawn thereon is put on the interlayer resininsulating layer 50 and exposure is conducted (see FIG. 15(B)).

(6) Development is conducted by spraying a DMTG solution and a heatprocess is conducted, thereby providing an interlayer resin insulatinglayer 50 having openings 48 each having a diameter of 85 μm for viaholes (see FIG. 15(C)).

(7) The surface of the interlayer resin insulating layer 50 is roughenedwith a permanganic acid or a chromic acid, thereby forming a roughsurface 50α (see FIG. 15(D)). Since following steps are the same asthose in the first embodiment stated above, no description will be giventhereto. The thickness of the rough surface 50α is preferably in therange of 0.05 to 5 μm.

The results of estimating the semiconductor devices in the above-statedembodiment and semiconductor devices in comparison examples whilecontaining the devices in the multilayer printed circuit boards in thefirst embodiment and the first modification are shown in tables of FIGS.17 and 18.

Comparison Example 1

In comparison example 1, a semiconductor device is the same as that inthe first embodiment. However, in the comparison example 1, notransition layers are formed and die pads are directly embedded into amultilayer printed circuit board.

Comparison Example 2

In comparison example 2, stud bumps described in Japanese PatentLaid-Open No. 9-321408 are formed and embedded into a multilayer printedcircuit board.

Estimation items are as follows:

({circle around (1)}) It is determined whether or not the die pads arediscolored or dissolved by visual observation.

({circle around (2)}) It is examined whether or not via hole openingscan be formed by examining whether openings each having a diameter of 60μm can be formed by laser using the multilayer printed circuit boardmanufacturing method in the first embodiment or by examining whetheropenings each having a diameter of 85 μm can be formed by photoetchingusing the multilayer printed circuit board manufacturing method in thefirst modification.

({circle around (3)}) Connection resistances between die pads and viaholes are measured.

In case of the semiconductor devices in the first to thirdmodifications, appropriate results were obtained. In case of thecomparison examples 1 and 2, however, there occurred problems such asvia hole formation defects, connection defects or resistance valueincrease.

With the structure of the first embodiment, the IC chip and the printedcircuit board can be connected to each other without using lead members.Due to this, resin sealing becomes unnecessary. Furthermore, since nodefects resulting from the lead members and sealing resin occur,connection characteristic and reliability are improved. Besides, sincethe pads of the IC chip are directly connected to the conductive layersof the printed circuit board, it is possible to improve electricalcharacteristic.

Moreover, compared with the conventional IC chip mounting method, thewiring length from the IC chip to the substrate to the externalsubstrate can be advantageously shortened and loop inductance can beadvantageously reduced. Also, the degree of freedom for wiring formationincreases to the extent that BGA's and PGA's can be provided.

Second Embodiment

The second embodiment of the present invention will be describedhereinafter with reference to the drawings.

The constitution of a multilayer printed circuit board containingtherein a semiconductor device (or an IC chip) 20 in the secondembodiment will be described.

As shown in FIG. 24, the multilayer printed circuit board 10 comprises aheat sink 30D on which the IC chip 20 in the first embodiment statedabove with reference to FIG. 3(B) is mounted, a core substrate 31containing therein the IC chip 20, an interlayer resin insulating layer50 and an interlayer resin insulating layer 150. Via holes 60 andconductor circuits 58 are formed on the interlayer resin insulatinglayer 50. Via holes 160 and conductor circuits 158 are formed on theinterlayer resin insulating layer 150.

A solder resist layer 70 is provided on the interlayer resin insulatinglayer 150. Solder bumps 76 for connecting to an external substrate suchas a daughter board or a mother board, which is not shown in FIG. 24,are provided on the conductor circuits 158 under the openings 71 of thesolder resist layer 70, respectively.

The heat sink 30D is made of ceramic such as aluminum nitride, aluminaor mullite, or metal such as aluminum alloy, copper or phosphor bronze.Here, the aluminum alloy having heat conductivity or a copper foil bothsides of which have been subjected to a roughening process isappropriate. In this embodiment, the heat sink 30D is attached to therear surface of the IC chip 20 embedded into the core substrate 31,thereby emitting heat generated in the IC chip 20, preventing the coresubstrate 31 and the interlayer resin insulating layers 50 and 150formed on the core substrate 31 from warping and preventing the breakageof the via holes 60, 160 and the conductor circuits 58 and 158 on theinterlayer resin insulating layers. Thus, the reliability of wiringsenhances.

It is noted that the IC chip 20 is attached to the heat sink 30D byconductive adhesive 29. The conductive adhesive 29 has resin containingmetallic powder such as copper, silver, gold or aluminum and has highheat conductivity, so that the heat generated in the IC chip 20 can beefficiently emitted toward the heat sink 30D. Here, the conductiveadhesive is used to attach the IC chip 20 to the heat sink 30D; however,various adhesives are available as long as they have high heatconductivity.

In the multilayer printed circuit board 10 in this embodiment, the ICchip 20 is integrated into the core substrate 31 and transition layers38 are provided on the respective pads 22 of the IC chip 20. Due tothis, it is possible to electrically connect the IC chip to themultilayer printed circuit board (or package substrate) without usinglead members and a sealing resin. Further, since the transition layers38 are formed on the IC chip portion, the IC chip portion is flattenedand the upper interlayer insulating layer 50 is, therefore, flattened tothereby provide uniform film thickness. Further, because of thetransition layers, it is possible to maintain the stability of shapeeven if the via holes 60 provided in the upper layer are formed.

Furthermore, by providing the transition layers 38 made of copper on therespective die pads 22, it is possible to prevent resin residues on thedie pads 22 and to prevent the die pads 22 from being discolored ordissolved even after impregnating the multilayer printed circuit boardin an acid, an oxidizer or an etching solution in a later step orconducting various annealing steps. Thus, connection characteristicbetween the die pads of the IC chip and the via holes and reliabilitycan be improved. Furthermore, by interposing the transition layers 38each having a diameter of 60 μm or more on the respective pads 22 eachhaving a diameter of 40 μm, it is possible to ensure connecting the viaholes each having a diameter of 60 μm.

Next, the method of manufacturing the multilayer printed circuit boarddescribed above with reference to FIG. 24 will be described withreference to FIGS. 19 to 23.

(1) A conductive adhesive 29 is applied onto a plate-shaped heat sink30D (see FIG. 19(A)) made of ceramic such as aluminum nitride, aluminaor mullite, or aluminum alloy, phosphor bronze or the like (see FIG.19(B)). The conductive adhesive is formed to have a thickness of 10 to20 μm using paste containing copper particles having a mean particlediameter of 2 to 5 μm.(2) IC chips 20 in the first embodiment, the first, second or thirdmodification of the first embodiment described above are mounted on theheat sink 30D (see FIG. 19(C)).(3) Next, the heat sink 30D to which the IC chips 20 have been attachedis mounted on a stainless (SUS) press plate 100A. A prepreg buildup body31α having a thickness of 0.5 mm and constituted by building up uncuredprepregs each having a core material such as glass cloths or the likeand impregnated with a resin such as a BT (Bismaleimide-Triazine) resinor epoxy, is mounted on the heat sink 30D (see FIG. 20(A)). Throughholes 32 are provided in the prepreg buildup body 31α at the positionsof the IC chips 20 in advance. While prepregs each having a corematerial impregnated with a resin are employed herein, it is alsopossible to employ a resin substrate without a core material.Alternatively, a sheet having a core material impregnated with variousthermosetting resins or a thermosetting resin and a thermoplastic resincan be used instead of the prepregs.(4) The above-stated buildup body is pressurized from vertical directionby the stainless (SUS) press plates 100A and 100B. At this moment, anepoxy resin 31β is exuded from the prepregs 31α, filled into the spacesbetween the through holes 32 and the IC chips 20 and covers the uppersurfaces of IC chips 20. As a result, the upper surfaces of the IC chips20 and the prepreg buildup body 31α are completely flattened (see FIG.20(B)). Due to this, when forming buildup layers in a step to bedescribed later, via holes and wirings can be appropriately formed andthe wiring reliability of the multilayer printed circuit board can bethereby improved.(5) Thereafter, heat is applied to cure the epoxy resin of the prepregs,thereby forming a core substrate 31 containing therein the IC chips 20(see FIG. 20(C)).(6) A thermosetting resin sheet having a thickness of 50 μm isvacuum-compression laminated onto the substrate which has gone throughthe above-stated steps at a pressure of 5 kg/cm² while raisingtemperature to 50 to 150° C., thereby providing an interlayer resininsulating layer 50 made of an epoxy resin (see FIG. 21(A)). The degreeof vacuum at the time of vacuum compression is 10 mmHg.(7) Next, using CO₂ gas laser having a wavelength of 10.4 μm, via holeopenings 48 each having a diameter of 60 μm are provided in theinterlayer resin insulating layer 50 under the conditions of a beamdiameter of 5 mm, a top hat mode, a pulse width of 5.0 microseconds, amask hole diameter of 0.5 mm and one shot (see FIG. 21(B)). Using achromic acid or a permanganic acid, resin residues in the openings 48are removed. By providing a transition layer 38 made of copper on eachdie pad 22, it is possible to prevent resin residues on the pad 22,thereby improving connection characteristic between the pad 22 and a viahole 60 to be described later and improving reliability. Furthermore, byinterposing the transition layer 38 having a diameter of 60 μm or moreon the die pad 22 having a diameter of 40 μm, it is possible to ensureconnecting the via hole opening 48 having a diameter of 60 μm. While theresin residues are removed by using an oxidizer such as a chromic acid,a de-smear process can be also conducted using oxygen plasma.(8) Next, the surface of the interlayer resin insulating layer 50 isroughened with a permanganic acid, thereby forming a rough surface 50α(see FIG. 21(C)).(9) Next, an electroless plated film 52 is provided on the interlayerresin insulating layer 50 on which the rough surface 50α has been formed(see FIG. 22(A)). Copper or nickel can be used for electroless plating.The thickness of the electroless plated film is preferably in the rangeof 0.3 μm to 1.2 μm. If the thickness is less than 0.3 μm, a metallicfilm cannot be formed on the interlayer resin insulating layer. If thethickness exceeds 1.2 μm, a metallic film is left as a result ofetching, easily causing short-circuit among conductors. The plated filmis formed with the same plating solution as that in the first embodimentunder the same plating conditions as those in the first embodiment.

Alternatively, an Ni/Cu metallic alloy 52 is formed on the surface ofthe interlayer resin insulating layer 50 by conducting sputtering withthe Ni—Cu alloy as a target under the conditions of an air pressure of0.6 Pa, a temperature of 80° C., power of 200 W and a duration of 5minutes with the same device as that used for the above-stated plasmaprocess. At this time, the thickness of the formed Ni/Cu alloy layer 52is 0.2 μm.

(10) A commercially available photosensitive dry film is bonded to thesubstrate 30 which has gone through the above processes, a photomaskfilm is mounted, exposure is performed at 100 mj/cm² and then adevelopment process is conducted with 0.8% sodium carbonate, therebyproviding a plating resist 54 having a thickness of 20 μm. Next,electroplating is conducted under the same conditions as in the firstembodiment to thereby form an electroplated film 56 having a thicknessof 15 μm (see FIG. 22(B)). An additive in the electroplating solution isKapalacid HL manufactured by Atotech Japan.(11) After separating and removing the plating resist 54 with 5% NaOH,the plated film layer 52 under the plating resist is dissolved andremoved by etching using a mixture solution of a nitric acid, a sulfuricacid and a hydrogen peroxide, conductor circuits 58 each comprising theplated film layer 52 and the electroplated film 56 and having athickness of 16 μm and via holes 60 are formed and etched by an etchingsolution containing a cupric salt complex and an organic acid, therebyforming rough surfaces 58α and 60α (see FIG. 22(C)). In this embodiment,as stated above with reference to FIG. 20(C), the surface of the coresubstrate 31 is formed completely smoothly, so that the IC chips 20 canbe appropriately connected to the transition layers 38 through the viaholes 60. Due to this, the reliability of the multilayer printed circuitboard can be improved.(12) Next, the steps of (6) to (11) stated above are repeated, therebyforming an upper interlayer resin insulating layer 150 and conductorcircuits 158 (including via holes 160) (see FIG. 23(A)).(13) Then, the same solder resist composition (or organic resininsulating material) as that in the first embodiment is obtained.(14) Next, the above-stated solder resist composition is applied to thesubstrate 30 to have a thickness of 20 μm and a drying process isconducted at 70° C. for 20 minutes and 70° C. for 30 minutes. Then, aphotomask having a pattern of solder resist opening portions drawnthereon and a thickness of 5 mm is made hermetic contact with the solderresist layer 70, exposure is performed with ultraviolet rays with 1000mj/cm² and then a development process is performed with a DMTG solution,thereby forming openings 71 each having a diameter of 200 μm (see FIG.23(B)).(15) Next, a nickel plated layer 72 having a thickness of 5 μm is formedon each opening portion 71 of the substrate on which the solder resistlayer (or organic resin insulating layer) 70 has been formed. Further, agold plated layer 74 having a thickness of 0.03 μm is formed on thenickel plated layer 72, thereby forming solder pads 75 on the respectiveconductor circuits 158 (see FIG. 23(C)).(16) Thereafter, a solder paste is printed the solder paste on theopening portions 71 of the solder resist layer 70 and reflow isconducted at 200° C., thereby forming solder bumps 76. Finally, the heatsink 30D is divided into pieces by dicing or the like, thereby obtainingmultilayer printed circuit boards 10 (see FIG. 24).

First Modification of Second Embodiment

Next, description will be given to a multilayer printed circuit boardaccording to the first modification of the second embodiment withreference to FIG. 26.

In the second embodiment stated above, description has been given to acase where the BGA's are arranged. In the first modification, which isalmost the same as the second embodiment, the multilayer printed circuitboard is constituted in a PGA type for establishing connection throughconductive connection pins 96 as shown in FIG. 26. Also, via holes areformed by laser in the above-stated second embodiment, whereas via holesare formed by photoetching in the first modification.

The method of manufacturing the multilayer printed circuit boardaccording to the first modification will be described with reference toFIG. 25.

(4) As in the case of the second embodiment, a thermosetting epoxy resin50 having a thickness of 50 μm is applied to the substrate which hasgone through the steps (1) to (3) stated above (see FIG. 25(A)).

(5) Next, a photomask film 49 having black circles 49 a corresponding tovia hole formed positions drawn thereon is put on the interlayer resininsulating layer 50 and exposure is conducted (see FIG. 25(B)).

(6) Development is conducted by spraying a DMTG solution and a heatprocess is conducted, thereby providing an interlayer resin insulatinglayer 50 having openings 48 each having a diameter of 85 μm for viaholes (see FIG. 25(C)).

(7) The surface of the interlayer resin insulating layer 50 is roughenedwith a permanganic acid or a chromic acid, thereby forming a roughsurface 50α (see FIG. 25(D)). Since following steps are the same asthose in the second embodiment stated above, no description will begiven thereto.

Second Modification of Second Embodiment

Next, the method of a multilayer printed circuit board according to thesecond modification of the second embodiment will be described.

In the first modification stated above, the core substrate is formed outof prepregs. In the second modification, by contrast, a resin substrateobtained by curing prepregs is fixed to a heat sink 30D by prepregs.

The method of a multilayer printed circuit board according to the secondmodification will be described with reference to FIG. 27.

(1) IC chips 20 are attached to a heat sink 30D made of a copper foilwhich both sides are roughened through conductive adhesive 29 and theheat sink 30D is mounted on a stainless (SUS) press plate 100A. Then,uncured prepregs (0.2 mm) 31α each having a core material such as glasscloths or the like and impregnated with a resin such as a BT(Bismaleimide-Triazine) resin or epoxy, are mounted on the heat sink30D. Further, resin substrates (0.4 mm) 31γ each having the above-statedprepregs built up and cured are mounted on the prepregs 31α (see FIG.27(A)). Through holes 32 are provided in the prepregs 31α and the resinsubstrates 31γ in advance at the positions of the IC chips 20.(2) The above-stated buildup body is pressurized from vertical directionby the stainless (SUS) press plates 100A and 100B. At this moment, anepoxy resin 31 is exuded from the prepregs 31α, filled into the spacesbetween the through holes 32 and the IC chips 20 and covers the uppersurfaces of IC chips 20. As a result, the upper surfaces of the IC chips20 and the resin substrates 31γ are completely flattened (see FIG.27(B)). Due to this, when forming buildup layers in a step to bedescribed later, via holes and wirings can be appropriately formed andthe wiring reliability of the multilayer printed circuit board can bethereby improved.(3) Thereafter, heat is applied to cure the epoxy resin of the prepregs,thereby forming a core substrate 31 containing therein the IC chips 20(see FIG. 27(C)). Since following steps are the same as those in thesecond embodiment, no description will be given thereto.

In the second embodiment, the heat sink is attached to the rear surfacesof the IC chips embedded in the core substrate, thereby allow heatgenerated in the IC chip to be discharged. By doing so, it is possibleto prevent the core substrate and interlayer resin insulating layersformed on the core substrate from warping, and prevent the breakage ofthe via holes and the conductor circuits on the interlayer resininsulating layers.

Furthermore, with the structure of the present invention, the IC chipcan be connected to the printed circuit board without using leadmembers. Due to this, resin sealing becomes unnecessary. Also, since nodefects resulting from the lead members and sealing resin occur,connection characteristic and reliability are improved. Besides, sincethe pads of the IC chip are directly connected to the conductive layersof the printed circuit board, it is possible to improve electricalcharacteristic.

Moreover, compared with the conventional IC chip mounting method, thewiring length from the IC chip to the substrate to the externalsubstrate can be advantageously shortened and loop inductance can beadvantageously reduced.

Third Embodiment

The third embodiment of the present invention will be describedhereinafter with reference to the drawings.

As shown in FIG. 33, a multilayer printed circuit board 10 in the thirdembodiment comprises a core substrate 30 containing therein an IC chip20, an interlayer resin insulating layer 50 and an interlayer resininsulating layer 150. Via holes 60 and conductor circuits 58 are formedon the interlayer resin insulating layer 50. Via holes 160 and conductorcircuits 158 are formed on the interlayer resin insulating layer 150.

A solder resist layer 70 is provided on the interlayer resin insulatinglayer 150. Solder bumps 76 for connecting to an external substrate,which is not shown, such as a daughter board or a mother board areprovided on the conductor circuit 158 under the opening portions 71 ofthe solder resist layer 70.

In case of the multilayer printed circuit board 10 in the thirdembodiment, the IC chip 20 is integrated into a core substrate 30 andtransition layers 38 are provided on the respective pads 22 of the ICchip 20. Due to this, it is possible to connect the IC chip to themultilayer printed circuit board (or package substrate) without usinglead members and a sealing resin. Also, since the transition layers 38are formed on the IC chip portion, the IC chip portion is flattened andthe upper interlayer resin insulating layer 50 is flattened accordingly,thereby providing uniform film thickness. Further, the transition layersallow maintaining shape even if the upper via holes 60 are formed.

Moreover, by providing the transition layers 38 made of copper on therespective die pads 22, it is possible to prevent resin residues on thedie pads 22 and to prevent the die pads 22 from being discolored ordissolved even after impregnating the multilayer printed circuit boardin an acid, an oxidizer or an etching solution in a later step orconducting various annealing steps. Thus, connection characteristicbetween the die pads of the IC chip and the via holes and reliabilitycan be improved. Furthermore, by interposing the transition layers 38each having a diameter of 60 μm or more on the respective pads 22 eachhaving a diameter of 40 μm, it is possible to ensure connecting the viaholes each having a diameter of 60 μm.

Next, the method of manufacturing the multilayer printed circuit boardaccording to the third embodiment described above with reference to FIG.33 will be described with reference to FIGS. 28 to 32.

(1) An insulating resin substrate 30A, in which prepregs each having acore material made of glass cloths or the like and impregnated with aresin such as BT (Bismaleimide-Triazine) resin or epoxy are built up andcured, is used as a starting material. First, throughholes 32 forcontaining therein IC chips are formed in the insulating resin substrate30A (see FIG. 28(A)). While the resin substrate 30A having the corematerial impregnated with the resin is used herein, it is also possibleto use a resin substrate without a core material.(2) Thereafter, IC chips 20 according to the manufacturing method in thefirst embodiment stated above are contained in the through holes 32 ofthe insulating resin substrate 30A (see FIG. 28(B)).(3) Then, the insulating resin substrate 30A containing therein the ICchips 20 and an insulating resin substrate (or core substrate) 30B, inwhich prepregs each having a core material made of glass cloths or thelike and impregnated with a resin such as epoxy are built up and curedand which has a thickness of 0.2 mm, are built up while interposinguncured prepregs 30C (each having a thickness of 0.1 mm) each having acore material such as glass cloths or the like and impregnated with aresin such as an epoxy resin between the substrates 30A and 30C (seeFIG. 28(C)). While the resin substrate 30B having the core materialimpregnated with the resin is used herein, it is also possible to use aresin substrate without a core material. Alternatively, instead of theprepregs, a sheet having a core material impregnated with various typesof thermosetting resins or a combination of a thermosetting resin and athermoplastic resin can be used.(4) The above-stated buildup body is pressurized from vertical directionby stainless (SUS) press plates 100A and 100B. At this moment, an epoxyresin 31α is exuded from the prepregs 31C, filled into the spacesbetween the through holes 32 and the IC chips 20 and covers the uppersurfaces of IC chips 20. As a result, the upper surfaces of the IC chips20 and the insulating resin substrate are completely flattened (see FIG.29(A)). Due to this, when forming buildup layers in a step to bedescribed later, via holes and wirings can be appropriately formed andthe wiring reliability of the multilayer printed circuit board can bethereby improved.(5) Thereafter, heat is applied to cure the uncured epoxy resin 30 a,thereby forming a core substrate 30 containing therein the IC chips 20(see FIG. 29(B)).(6) A thermosetting resin sheet having a thickness of 50 μm isvacuum-compression laminated onto the substrate which has gone throughthe above-stated steps at a pressure of 5 kg/cm² while raisingtemperature to 50 to 150° C., thereby providing an interlayer resininsulating layer 50 (see FIG. 29(C)). The degree of vacuum at the timeof vacuum compression is 10 mmHg.(7) Next, using CO₂ gas laser having a wavelength of 10.4 μm, via holeopenings 48 each having a diameter of 60 μm are provided in theinterlayer resin insulating layer 50 under the conditions of a beamdiameter of 5 mm, a top hat mode, a pulse width of 5.0 microseconds, amask hole diameter of 0.5 mm and one shot (see FIG. 30(A)). Using anoxidizer such as a chromic acid or a permanganic acid, resin residues inthe openings 48 are removed. By providing a transition layer 38 made ofcopper on each die pad 22, it is possible to prevent resin residues onthe pad 22, thereby improving connection characteristic between the pad22 and a via hole 60 to be described later and improving reliability.Furthermore, by interposing the transition layer 38 having a diameter of60 μm or more on the die pad 22 having a diameter of 40 μm, it ispossible to ensure connecting the via hole opening 48 having a diameterof 60 μm. While the resin residues are removed by using the oxidizerherein, a de-smear process can be also conducted using oxygen plasma.(8) Next, the surface of the interlayer resin insulating layer 50 isroughened with a permanganic acid, thereby forming a rough surface 50 a(see FIG. 30(B)).(9) Next, an electroless plated film 52 is provided on the interlayerresin insulating layer 50 on which the rough surface 50 a has beenformed (see FIG. 30(C)). Copper or nickel can be used for electrolessplating. The thickness of the electroless plated film is preferably inthe range of 0.3 μm to 1.2 μm. If the thickness is less than 0.3 μm, ametallic film cannot be formed on the interlayer resin insulating layer.If the thickness exceeds 1.2 μm, a metallic film is left as a result ofetching, easily causing short-circuit among conductors. The plated filmis formed with the same plating solution as that in the first embodimentunder the same plating conditions as those in the first embodiment.

Alternatively, an Ni/Cu metallic alloy 52 is formed on the surface ofthe interlayer resin insulating layer 50 by conducting sputtering withthe Ni—Cu alloy as a target under the conditions of an air pressure of0.6 Pa, a temperature of 80° C., power of 200 W and a duration of 5minutes with the same device as that used for the above-stated plasmaprocess. At this time, the thickness of the formed Ni/Cu alloy layer 52is 0.2 μm.

(10) A commercially available photosensitive dry film is bonded to thesubstrate 30 which has gone through the above processing steps, aphotomask film is mounted, exposure is performed at 100 mj/cm² and thena development process is conducted with 0.8% sodium carbonate, therebyproviding a plating resist 54 having a thickness of 20 μm. Next,electroplating is conducted under the same conditions as those in thefirst embodiment to thereby form an electroplated film 56 having athickness of 15 μm. (see FIG. 31(A)).(11) After separating and removing the plating resist 54 with 5% NaOH,the plated film layer 52 under the plating resist is dissolved andremoved by etching using a mixture solution of a nitric acid, a sulfuricacid and a hydrogen peroxide, conductor circuits 58 each comprising theplated film layer 52 and the electroplated film 56 and having athickness of 16 μm and via holes 60 are formed and etched by an etchingsolution containing a cupric salt complex and an organic acid, therebyforming rough surfaces 58α and 60α (see FIG. 31(B)). In this embodiment,as stated above with reference to FIG. 29(A), the surface of the coresubstrate 30 is formed completely smoothly, so that the IC chips 20 canbe appropriately connected to the transition layers 38 through the viaholes 60. Due to this, the reliability of the multilayer printed circuitboard can be improved.(12) Next, the steps of (6) to (11) stated above are repeated, therebyforming an upper interlayer resin insulating layer 150 and conductorcircuits 158 (including via holes 160) (see FIG. 31(C)).(13) Then, a solder resist composition (or organic resin insulatingmaterial) prepared in the same manner as that in the first embodiment isobtained.(14) Next, the above-stated solder resist composition is applied to thesubstrate 30 to have a thickness of 20 μm and a drying process isconducted at 70° C. for 20 minutes and 70° C. for 30 minutes. Then, aphotomask having a pattern of solder resist opening portions drawnthereon and a thickness of 5 mm is made hermetic contact with the solderresist layer 70, exposure is performed with ultraviolet rays with 1000mj/cm² and then a development process is performed with a DMTG solution,thereby forming openings 71 each having a diameter of 200 μm (see FIG.32(A)).(15) Next, a nickel plated layer 72 having a thickness of 5 μm is formedon each opening portion 71 of the substrate on which the solder resistlayer (or organic resin insulating layer) 70 has been formed. Further, agold plated layer 74 having a thickness of 0.03 μm is formed on thenickel plated layer 72, thereby forming solder pads 75 on the respectiveconductor circuits 158 (see FIG. 32(B)).(16) Thereafter, a solder paste is printed on the opening portions 71 ofthe solder resist layer 70 and reflow is conducted at 200° C., therebyforming solder bumps 76. The resultant substrate is divided into piecesby dicing or the like, thereby obtaining a plurality of pieces ofmultilayer printed circuit boards 10 (see FIG. 32(C)). While themultilayer printed circuit board is halved for the convenience ofdescription in FIG. 32(C), many IC chip-integrated multilayer printedcircuit boards are simultaneously manufactured by dividing the substrateinto 16, 32, 64 pieces or the like.

In the third embodiment, the steps of FIG. 28(A) to FIG. 32 (B) statedabove, a multilayer printed circuit board into which semiconductordevices are integrated is manufactured for obtaining multiple multilayerprinted circuit boards. Then, as shown in FIG. 32(C), the multilayerprinted circuit board is cut into pieces, thereby obtaining a pluralityof multilayer printed circuit boards. Due to this, it is possible toefficiently manufacture highly reliable multilayer printed circuitboards 10 (see FIG. 33).

First Other Example of Third Embodiment

A multilayer printed circuit board according to the other example of thethird embodiment will be described with reference to FIG. 35.

In the third embodiment stated above, description has been given to acase where the BGA's are arranged. In the first other example, which isalmost the same as the third embodiment, the multilayer printed circuitboard is constituted in a PGA type for establishing connection throughconductive connection pins 96 as shown in FIG. 35. Also, via holes areformed by laser in the above-stated third embodiment, whereas via holesare formed by photoetching in the first another example.

The method of manufacturing the multilayer printed circuit boardaccording to the first other example will be described with reference toFIG. 34.

(4) As in the case of the third embodiment, a thermosetting epoxy resin50 having a thickness of 50 μm is applied to the substrate which hasgone through the steps (1) to (3) stated above (see FIG. 34(A)).

(5) Next, a photomask film 49 having black circles 49 a corresponding tovia hole formed positions drawn thereon is put on the interlayer resininsulating layer 50 and exposure is conducted (see FIG. 34(B)).

(6) Development is conducted by spraying a DMTG solution and a heatprocess is conducted, thereby providing an interlayer resin insulatinglayer 50 having openings 48 each having a diameter of 85 μm for viaholes (see FIG. 34(C)).

(7) The surface of the interlayer resin insulating layer 50 is roughenedwith a permanganic acid or a chromic acid, thereby forming a roughsurface 50α (see FIG. 34(D)). Since following steps are the same asthose in the third embodiment stated above, no description will be giventhereto.

First Modification of Third Embodiment

Next, the constitution of a multilayer printed circuit board containingtherein a semiconductor device (or an IC chip) 20 in the firstmodification of the third embodiment will be described.

In case of the multilayer printed circuit board 10 in the thirdembodiment described above with reference to FIG. 33, the IC chip isembedded into the core substrate. In the first modification, bycontrast, as shown in FIG. 41, a heat sink 30D is attached to the rearsurface of an IC chip 20. The multilayer printed circuit board 10comprises the heat sink 30D, a core substrate 31 containing therein theIC chip 20, an interlayer resin insulating layer 50 and an interlayerresin insulating layer 150 above the IC chip 20. Via holes 60 andconductor circuits 58 are formed on the interlayer resin insulatinglayer 50. Via holes 160 and conductor circuits 158 are formed on theinterlayer resin insulating layer 150.

A solder resist layer 70 is provided on the interlayer resin insulatinglayer 150. Solder bumps 76 for connecting to an external substrate suchas a daughter board or a mother board, which is not shown, are providedon the conductor circuits 158 under the openings 71 of the solder resistlayer 70, respectively.

The heat sink 30D is made of ceramic such as aluminum nitride, aluminaor mullite, or metal such as aluminum alloy, copper or phosphor bronze.Here, the aluminum alloy having heat conductivity or a copper foil bothsides of which have been subjected to a roughening process isappropriate. In this embodiment, the heat sink 30D is attached to therear surface of the IC chip 20 embedded into the core substrate 31,thereby emitting heat generated in the IC chip 20, preventing the coresubstrate 31 and the interlayer resin insulating layers 50 and 150formed on the core substrate 31 from warping and preventing the breakageof the via holes 60, 160 and the conductor circuits 58 and 158 on theinterlayer resin insulating layers. Thus, the reliability of wiringsenhances.

It is noted that the IC chip 20 is attached to the heat sink 30D byconductive adhesive 29. The conductive adhesive 29 has resin containingmetallic powder such as copper, silver, gold or aluminum and has highheat conductivity, so that the heat generated in the IC chip 20 can beefficiently emitted toward the heat sink 30D. Here, the conductiveadhesive is used to attach the IC chip 20 to the heat sink 30D; however,various adhesives are available as long as they have high heatconductivity.

In the multilayer printed circuit board 10 in the first modification ofthe third embodiment, the IC chip 20 is integrated into the coresubstrate 30 and transition layers 38 are provided on the respectivepads 22 of the IC chip 20. Due to this, it is possible to electricallyconnect the IC chip to the multilayer printed circuit board (or packagesubstrate) without using lead members and a sealing resin. Further,since the transition layers 38 are formed on the IC chip portion, the ICchip portion is flattened and the upper interlayer insulating layer 50is, therefore, flattened to thereby provide uniform film thickness.Further, because of the transition layers, it is possible to maintainthe stability of shape even if the via holes 60 provided in the upperlayer are formed.

Furthermore, by providing the transition layers 38 made of copper on therespective die pads 22, it is possible to prevent resin residues on thedie pads 22 and to prevent the die pads 22 from being discolored ordissolved even after impregnating the multilayer printed circuit boardin an acid, an oxidizer or an etching solution in a later step orconducting various annealing steps. Thus, connection characteristicbetween the die pads of the IC chip and the via holes and reliabilitycan be improved. Furthermore, by interposing the transition layers 38each having a diameter of 60 μm or more on the respective pads 22 eachhaving a diameter of 40 μm, it is possible to ensure connecting the viaholes each having a diameter of 60 μm.

Next, the method of manufacturing the multilayer printed circuit boarddescribed above with reference to FIG. 41 will be described withreference to FIGS. 36 to 40.

(1) A conductive adhesive 29 is applied onto a plate-shaped heat sink30D (see FIG. 36(A)) made of ceramic such as aluminum nitride, aluminaor mullite, or aluminum alloy, phosphor bronze or the like (see FIG.36(B)). The conductive adhesive is formed to have a thickness of 10 to20 μm using paste containing copper particles having a mean particlediameter of 2 to 5 μm.(2) IC chips 20 in the first to fourth manufacturing methods statedabove with reference to FIG. 3(B) are mounted on the heat sink 30D (seeFIG. 36(C)).(3) Next, the heat sink 30D to which the IC chips 20 have been attachedis mounted on a stainless (SUS) press plate 100A. A prepreg buildup body31α having a thickness of 0.5 mm and constituted by building up uncuredprepregs each having a core material such as glass cloths or the likeand impregnated with a resin such as a BT (Bismaleimide-Triazine) resinor epoxy, is mounted on the heat sink 30D (see FIG. 37(A)). Throughholes 32 are provided in the prepreg buildup body 31α at the positionsof the IC chips 20 in advance. While prepregs each having a corematerial impregnated with a resin are employed herein, it is alsopossible to employ a resin substrate without a core material.Alternatively, a sheet having a core material impregnated with variousthermosetting resins or a combination of a thermosetting resin and athermoplastic resin can be used instead of the prepregs.(4) The above-stated buildup body is pressurized from vertical directionby the stainless (SUS) press plates 100A and 100B. At this moment, anepoxy resin 31β is exuded from the prepregs 31α, filled into the spacesbetween the through holes 32 and the IC chips 20 and covers the uppersurfaces of IC chips 20. As a result, the upper surfaces of the IC chips20 and the prepreg buildup body 31α are completely flattened (see FIG.37(B)). Due to this, when forming buildup layers in a step to bedescribed later, via holes and wirings can be appropriately formed andthe wiring reliability of the multilayer printed circuit board can bethereby improved.(5) Thereafter, heat is applied to cure the epoxy resin of the prepregs,thereby forming a core substrate 31 containing therein the IC chips 20(see FIG. 37(C)).(6) A thermosetting resin sheet having a thickness of 50 μm isvacuum-compression laminated onto the substrate which has gone throughthe above-stated steps at a pressure of 5 kg/cm² while raisingtemperature to 50 to 150° C., thereby providing an interlayer resininsulating layer 50 (see FIG. 38(A)). The degree of vacuum at the timeof vacuum compression is 10 mmHg.(7) Next, using CO₂ gas laser having a wavelength of 10.4 μm, via holeopenings 48 each having a diameter of 60 μm are provided in theinterlayer resin insulating layer 50 under the conditions of a beamdiameter of 5 mm, a top hat mode, a pulse width of 5.0 microseconds, amask hole diameter of 0.5 mm and one shot (see FIG. 38(B)). Using achromic acid, resin residues in the openings 48 are removed. Byproviding a transition layer 38 made of copper on each die pad 22, it ispossible to prevent resin residues on the pad 22, thereby improvingconnection characteristic between the pad 22 and a via hole 60 to bedescribed later and improving reliability. Furthermore, by interposingthe transition layer 38 having a diameter of 60 μm or more on the diepad 22 having a diameter of 40 μm, it is possible to ensure connectingthe via hole opening 48 having a diameter of 60 μm. While the resinresidues are removed by using a chromic acid, a de-smear process can bealso conducted using oxygen plasma.(8) Next, the surface of the interlayer resin insulating layer 50 isroughened with a permanganic acid, thereby forming a rough surface 50 a(see FIG. 38(C)).(9) Next, an electroless plated film 52 is provided on the interlayerresin insulating layer 50 on which the rough surface 50 a has beenformed (see FIG. 39(A)). Copper or nickel can be used for electrolessplating. The thickness of the electroless plated film is preferably inthe range of 0.3 μm to 1.2 μm. If the thickness is less than 0.3 μm, ametallic film cannot be formed on the interlayer resin insulating layer.If the thickness exceeds 1.2 μm, a metallic film is left as a result ofetching, easily causing short-circuit among conductors. The plated filmis formed with the same plating solution as that in the first embodimentunder the same plating conditions as those in the first embodiment.

Alternatively, an Ni/Cu metallic alloy 52 is formed on the surface ofthe interlayer resin insulating layer 50 by conducting sputtering withthe Ni—Cu alloy as a target using the same device as that used for theabove-stated plasma process. At this time, the thickness of the formedNi/Cu alloy layer 52 is 0.2 μm.

(10) A commercially available photosensitive dry film is bonded to thesubstrate 30 which has gone through the above processes, a photomaskfilm is mounted, exposure is performed at 100 mj/cm² and then adevelopment process is conducted with 0.8% sodium carbonate, therebyproviding a plating resist 54 having a thickness of 20 μm. Next,electroplating is conducted to thereby form an electroplated film 56having a thickness of 15 μm (see FIG. 39(B)).(11) After separating and removing the plating resist 54 with 5% NaOH,the plated film layer 52 under the plating resist is dissolved andremoved by etching using a mixture solution of a nitric acid, a sulfuricacid and a hydrogen peroxide, conductor circuits 58 each comprising theplated film layer 52 and the electroplated film 56 and having athickness of 16 μm and via holes 60 are formed and etched by an etchingsolution containing a cupric salt complex and an organic acid, therebyforming rough surfaces 58α and 60α (see FIG. 39(C)). In the firstmodification of the third embodiment, as stated above with reference toFIG. 37(C), the surface of the core substrate 31 is formed completelysmoothly, so that the IC chips 20 can be appropriately connected to thetransition layers 38 through the via holes 60. Due to this, thereliability of the multilayer printed circuit board can be improved.(12) Next, the steps of (6) to (11) stated above are repeated, therebyforming an upper interlayer resin insulating layer 150 and conductorcircuits 158 (including via holes 160) (see FIG. 40(A)).(13) Next, the same solder resist composition as that in the thirdembodiment is applied to the substrate 30 to have a thickness of 20 μmand a drying process is conducted at 70° C. for 20 minutes and 70° C.for 30 minutes. Then, a photomask having a pattern of solder resistopening portions drawn thereon and a thickness of 5 mm is made hermeticcontact with the solder resist layer 70, exposure is performed withultraviolet rays with 1000 mj/cm² and then a development process isperformed with a DMTG solution, thereby forming openings 71 each havinga diameter of 200 μm (see FIG. 40(B)).(14) Next, the substrate on which the solder resist layer (or organicresin insulating layer) 70 has been formed is immersed in the sameelectroless nickel plating solution as that in the third embodiment for20 minutes, thereby forming a nickel plated layer 72 having a thicknessof 5 μm on each opening portion 71. Further, the substrate is immersedin the same electroless gold plating solution as that in the thirdembodiment to form a gold plated layer 74 having a thickness of 0.03 μmis formed on the nickel plated layer 72, thereby forming solder pads 75on the respective conductor circuits 158 (see FIG. 40(C)).(15) Thereafter, a solder paste is printed on the opening portions 71 ofthe solder resist layer 70 and reflow is conducted at 200° C., therebyforming solder bumps 76. Finally, the heat sink 30D is divided intopieces by dicing or the like, thereby obtaining multilayer printedcircuit boards 10 (see FIG. 41).

First Other Example of First Modification of Third Embodiment

Next, description will be given to a multilayer printed circuit boardaccording to the first other example of the first modification of thethird embodiment with reference to FIG. 43.

In the first modification stated above, description has been given to acase where the BGA's are arranged. In the first other example, which isalmost the same as the first modification, the multilayer printedcircuit board is constituted in a PGA type for establishing connectionthrough conductive connection pins 96 as shown in FIG. 43. Also, viaholes are formed by laser in the above-stated first embodiment, whereasvia holes are formed by photoetching in the first another example.

The method of manufacturing the multilayer printed circuit boardaccording to the first other example will be described with reference toFIG. 42.

(4) As in the case of the first modification, a thermosetting epoxyresin 50 having a thickness of 50 μm is applied to the substrate whichhas gone through the steps (1) to (3) stated above (see FIG. 42(A)).

(5) Next, a photomask film 49 having black circles 49 a corresponding tovia hole formed positions drawn thereon is put on the interlayer resininsulating layer 50 and exposure is conducted (see FIG. 42(B)).

(6) Development is conducted by spraying a DMTG solution and a heatprocess is conducted, thereby providing an interlayer resin insulatinglayer 50 having openings 48 each having a diameter of 85 μm for viaholes (see FIG. 42(C)).

(7) The surface of the interlayer resin insulating layer 50 is roughenedwith a permanganic acid or a chromic acid, thereby forming a roughsurface 50α (see FIG. 42(D)). Since following steps are the same asthose in the second embodiment stated above, no description will begiven thereto.

Second Other Example of First Modification of Third Embodiment

Next, the method of a multilayer printed circuit board according to thesecond other example of the first modification of the third embodimentwill be described.

In the first modification and the first other example stated above, thecore substrate 30 is formed out of prepregs. In the second otherexample, by contrast, a resin substrate obtained by curing prepregs isfixed to a heat sink 30D by prepregs.

The method of a multilayer printed circuit board according to the secondother will be described with reference to FIG. 44.

(1) IC chips 20 are attached to a heat sink 30D made of a copper foilwhich both sides are roughened through conductive adhesive 29 and theheat sink 30D is mounted on a stainless (SUS) press plate 100A. Then,uncured prepregs (0.2 mm) 31α each having a core material such as glasscloths or the like and impregnated with a resin such as a BT(Bismaleimide-Triazine) resin or epoxy, are mounted on the heat sink30D. Further, resin substrates (0.4 mm) 31γ each having the above-statedprepregs built up and cured are mounted on the prepregs 31α (see FIG.44(A)). Through holes 32 are provided in the prepregs 31α and the resinsubstrates 31γ in advance at the positions of the IC chips 20.(2) The above-stated buildup body is pressurized from vertical directionby the stainless (SUS) press plates 100A and 100B. At this moment, anepoxy resin 31β is exuded from the prepregs 31α, filled into the spacesbetween the through holes 32 and the IC chips 20 and covers the uppersurfaces of IC chips 20. As a result, the upper surfaces of the IC chips20 and the resin substrates 31γ are completely flattened (see FIG.44(B)). Due to this, when forming buildup layers in a step to bedescribed later, via holes and wirings can be appropriately formed andthe wiring reliability of the multilayer printed circuit board can bethereby improved.(3) Thereafter, heat is applied to cure the epoxy resin of the prepregs,thereby forming a core substrate 31 containing therein the IC chips 20(see FIG. 44(C)). Since following steps are the same as those in thesecond embodiment, no description will be given thereto.

Second Modification of Third Embodiment

The constitution of a multilayer printed circuit board according to thesecond modification will be described with reference to FIG. 50 whichshows the cross section of a multilayer printed circuit board 10.

In the first modification stated above, one IC chip is contained in themultilayer printed circuit board. The multilayer printed circuit board10 according to the second modification as shown in FIG. 50, bycontrast, contains an IC chip (or CPU) 20A and an IC chip (or a cachememory) 20B in a core substrate 30. Then, as in the case of the thirdembodiment, interlayer resin insulating layers 50 and 150 are formed onthe core substrate 30. Via holes 60 and conductor circuits 58 are formedon the interlayer resin insulating layer 50. Via holes 160 and conductorcircuits 158 are formed on the interlayer resin insulating layer 150.

The IC chips 20A and 20B are covered with a passivation film 24 and diepads 22 constituting input/output terminals are provided in the openingsof the passivation film 24. Transition layers 38 are formed on therespective die pads 22 made of aluminum. Each transition layer 38 has athree-layer structure comprising the first thin film layer 33, thesecond thin film layer 36 and a thickening layer 37.

A solder resist layer 70 is provided on the interlayer resin insulatinglayer 150. Solder bumps 76 for connecting to an external substrate suchas a daughter board or a mother board, which is not shown, are providedon the conductor circuits 158 under the openings 71 of the solder resistlayer 70, respectively.

In the multilayer printed circuit board 10 in the second modification ofthe third embodiment, the IC chips 20A and 20B are integrated into acore substrate 30 in advance and the transition layers 38 are providedon the respective pads 22 of the IC chips 20A and 20B. Due to this, itis possible to electrically connect the IC chips to the multilayerprinted circuit board (or package substrate) without using lead membersand a sealing resin. Further, since the transition layers 38 are formedon the IC chip portions, the IC chip portions are flattened and aninterlayer insulating layer 50 provided above the chips is, therefore,flattened to thereby provide uniform film thickness. Further, because ofthe transition layers, it is possible to maintain the stability of shapeeven if via holes 60 provided in the upper layer are formed.

Furthermore, by providing the transition layers 38 made of copper on therespective die pads 22, it is possible to prevent resin residues on thedie pads 22 and to prevent the die pads 22 from being discolored ordissolved even after impregnating the multilayer printed circuit boardin an acid, an oxidizer or an etching solution in a later step orconducting various annealing steps. Thus, connection characteristicbetween the die pads of the IC chips and the via holes and reliabilitycan be improved. Besides, by interposing the transition layers 38 eachhaving a diameter of 60 μm or more on the respective pads 22 each havinga diameter of 40 μm, it is possible to ensure connecting the via holeseach having a diameter of 60 μm.

In the second modification of the third embodiment, the IC chip 20A fora CPU and the IC chip 20B for a cache memory are separately embeddedinto the printed circuit board. Since the IC chips can be moreeconomical if they are formed separately and the chips are locatedadjacent to each other, transmission delay or malfunction does notoccur. Besides, even if the design of the printed circuit board ischanged, there is no need to change the design of the IC chipsthemselves and the degree of freedom for formation can be increased.

An adhesive layer 34 is filled into the recess 32 of the printed circuitboard in the second modification of the third embodiment. Thus, it ispossible to couple the IC chips 20A and 20B in the recess 32 and theadhesive 34 can suppress the behaviors of the IC chips 20A and 20B andmaintain smoothness even after a heat history during a heat cycle andvia hole formation. Due to this, the connection portions between the ICchips and the via holes are not peeled or broken or the interlayerinsulating layers 50 and 150 do not crack. It is also possible toimprove reliability.

Next, the method of manufacturing the multilayer printed circuit boardaccording to the second modification of the third embodiment statedabove with reference to FIG. 50 will be described with reference toFIGS. 45 to 49. Here, in the first modification stated above, thetransition layers 38 are formed on the IC chip and then the IC chip iscontained in the core substrate. In the second modification, bycontrast, the IC chips are contained in the core substrate and then thetransition layers 38 are formed.

(1) First, an insulating resin substrate (or core substrate) 30 in whichprepregs each having a core material made of glass cloths or the likeand impregnated with a resin such as epoxy are built up, is used as astarting material (see FIG. 45(A)). Next, recesses 32 for containing ICchips are formed on one side of the core substrate 30 by counter boring(see FIG. 45(B)). While the recesses are provided by counter boringherein, it is also possible to or a core substrate having containingsections by laminating an insulating resin substrate having an openingportion and an insulating resin substrate without openings.(2) Then, an adhesive material 34 is applied to the recesses 32 using aprinting machine. At this time, potting instead of application may beconducted. Next, IC chips 20A and 20B are mounted on the adhesivematerial 34 (see FIG. 45(C)).(3) Then, the upper surfaces of the IC chips 20A and 20B are depressedor struck to thereby completely contain the IC chips 20A and 20B in therespective recesses 32 (see FIG. 45(D)). By doing so, the core substrate30 can be smoothed.(4) Thereafter, the entire surface of the core substrate 30 whichcontains the IC chips 20A and 20B therein is subjected to deposition orsputtering to form the conductive, first thin film layer 33 on theentire surface (see FIG. 45(E)). A metal used may be nickel, zinc,chromium, cobalt, titanium, gold, tin or copper or the like. Nickel,chromium or titanium is more preferable because it is capable ofsuppressing the entry of moisture into an interface, appropriate forfilm formation and in electrical characteristic. The thickness of thefirst thin film layer 33 is preferably 0.001 to 2.0 μm, more preferably,0.01 to 1.0 μm. In case of chromium, the thickness is preferably 0.1 μm.

Die pads 22 are covered with the first thin film layer 33, therebymaking it possible to improve the adhesiveness of transition layers andthe IC chips to the interfaces with the die pads 22. Also, by coveringthe die pad 22 with the metal, it is possible to prevent moisture fromentering the interfaces, to prevent the dissolution and erosion of thedie pads and to improve reliability. Further, the first thin film layer33 allows the die pads to connect with the IC chips by a mounting methodwithout using leads. Here, chromium or titanium is preferably used sinceit is possible to prevent the entry of moisture into the interfaces.

(5) The second thin film layer 36 is formed on the first thin film layer33 by sputtering, deposition or electroless plating (FIG. 46(A)). Ametal used herein may be nickel, copper, gold or silver or the like.Copper is preferable in view of electrical characteristic,inexpensiveness and the fact that a buildup conductor layer to be formedin a later step mainly comprises copper.

The reason for providing the second thin film layer is that anelectroplating lead for forming a thickening layer to be described latercannot be provided only with the first thin film layer. The second thinfilm layer 36 is used as a lead for thickening and preferably 0.01 to 5μm in thickness. If the thickness is smaller than 0.01 μm, the secondthin film layer cannot function as a lead. If the thickness exceeds 5μm, the first thin film layer under the second thin film layer is cutmore than the second thin film layer and gaps are generated between thefirst and second thin film layers during etching, thereby making theentry of moisture easier and deteriorating reliability. An optimumthickness is 0.1 to 3 μm.

(6) Thereafter, a resist is applied, exposure and development areconducted to provide a plating resist 35 while providing openings on theupper portions of the respective die pads of the IC chips, andelectroplating is conducted to thereby provide an electroplated film (orthickening film) 37 (see FIG. 46(B)). The thickening film can be formedout of nickel, copper, gold, silver, zinc or iron.

After removing the plating resist 35, the electroless plated, secondthin film layer 36 and first thin film layer 33 under the plating resist35 are etched away, thereby forming a transition layer 38 on each of thedie pads 22 of the IC chips (FIG. 46(C)). While each transition layer isformed by the plating resist herein, the transition layer may be formedon each die pad by, after uniformly forming an electroplated film on theelectroless plated, second thin film layer 36, forming an etchingresist, conducting exposure and development to expose the metal otherthan that of the transition layer, and conducting etching. The thicknessof the electroplated film is preferably in the range of 1 to 20 μm. Ifthe thickness exceeds that range, undercut may possibly occur during theetching to generate gaps in the interface between the transition layerto be formed and the via hole.

(7) Next, an etching solution is sprayed onto the substrate and thesurfaces of the transition layers 38 are etched, thereby forming roughsurfaces 38α (see FIG. 46(D)). The rough surfaces can be also formed byelectroless plating or an oxidization-reduction process. Each transitionlayer 38 has a three-layer structure comprising the first thin filmlayer 33, the second thin film layer 36 and the thickening film 37.(8) A thermosetting epoxy type resin sheet having a thickness of 50 μmis vacuum-compression laminated onto the substrate which has gonethrough the above-stated steps at a pressure of 5 kg/cm² while raisingtemperature to 50 to 150° C., thereby providing an interlayer resininsulating layer 50 (see FIG. 47(A)). The degree of vacuum at the timeof vacuum compression is 10 mmHg.(9) Next, using CO² gas laser having a wavelength of 10.4 μm, via holeopenings 48 each having a diameter of 80 μm are provided in theinterlayer resin insulating layer 50 under the conditions of a beamdiameter of 5 mm, a top hat mode, a pulse width of 5.0 μm, a mask holediameter of 0.5 mm and one shot (see FIG. 47(B)). Using a chromium acid,resin residues in the openings 48 are removed. By providing thetransition layer 38 made of copper on each die pad 22, it is possible toprevent resin residues on the die pad 22, thereby improving connectioncharacteristic between the die pad 22 and a via hole 60 to be describedlater and improving reliability. Furthermore, by interposing thetransition layer 38 having a diameter of 60 μm or more on each die pad22 having a diameter of about 40 μm, it is possible to ensure connectingthe via hole opening 48 having a diameter of 60 μm. While the resinresidues are removed by using a permanganic acid, a de-smear process canbe also conducted using oxygen plasma. While the openings 48 are formedby laser herein, the openings can be formed by conducting exposure anddevelopment processes.(10) Using an acid or an oxidizer, a rough surface 50α is formed on theinterlayer resin insulating layer 50 (see FIG. 47(C)). The rough surface50α is preferably formed in the range of 1 to 5 μm.(11) An electroless plated film 52 is provided on the interlayer resininsulating layer 50 on which the rough surface 50α has been formed (seeFIG. 48(A)). As a material for electroless plating, copper or nickel canbe used. The thickness of the electroless plated film is preferably inthe range of 0.3 μm to 1.2 μm. If the thickness is smaller than 0.3 μm,a metallic film cannot be often formed on the interlayer resininsulating layer. If the thickness exceeds 1.2 μm, the metallic filmremains after etching and short-circuit often occurs between conductors.The plated film is formed with the same plating solution as that in thefirst embodiment under the same plating conditions as those in the firstembodiment.(12) A commercially available photosensitive dry film is bonded to thesubstrate 30 which has been subjected to the above processes, a chromiumglass mask is mounted, exposure is performed at 40 mj/cm² and then adevelopment process is conducted with 0.8% sodium carbonate, therebyproviding a plating resist 54 having a thickness of 25 μm. Next,electroplating is conducted to form an electroplated film 56 having athickness of 18 μm (see FIG. 48(B)).(13) After peeling and removing the plating resist 54 with 5% NaOH, theplated film layer 52 under the plating resist is dissolved and removedby etching using a mixture solution of a nitric acid and hydrogenperoxide, conductor circuits 58 each comprising the plated film layer 52and the electroplated film 56 and having a thickness of 16 μm and viaholes 60 are formed and rough surfaces 58α and 60α are formed using anetching solution containing a cupric salt complex and an organic acid(see FIG. 48(C)). Alternatively, the rough surfaces can be formed byelectroless plating or an oxidization-reduction process.(14) Next, the steps of (9) to (13) stated above are repeated, therebyforming an upper interlayer resin insulating layer 150 and conductorcircuits 158 (including via holes 160) (see FIG. 49(A)).(15) Next, the same solder resist composition as that in the firstembodiment is applied to the substrate 30 to have a thickness of 30 μmand a drying process is conducted at 70° C. for 20 minutes and 70° C.for 30 minutes. Then, a photomask film having a pattern of the solderresist opening portions drawn thereon and a thickness of 5 mm is madehermetic contact with the solder resist layer 70, exposure is performedwith ultraviolet rays with 1000 mj/cm² and then a development process isperformed with a DMTG solution, thereby forming openings 71 each havingan opening diameter of 460 μm (see FIG. 49(B)).(16) Next, the substrate on which the solder resist layer (or organicresin insulating layer) 70 has been formed, is immersed in the sameelectroless nickel plating solution as that in the first embodiment, anda nickel plate layer 72 having a thickness of 5 μm is formed on eachopening portion 71. Then, the substrate is further immersed in theelectroless plating solution as that in the first embodiment and a goldplated layer 74 having a thickness of 0.03 μm is formed on the nickelplated layer 72, thereby forming a solder pad 75 on each conductorcircuit 158 (see FIG. 49(C)).(17) Thereafter, a solder paste is printed on the opening portions 71 ofthe solder resist layer 70 and reflow is conducted at 200° C., therebyforming solder bumps 76. Then, the resultant substrate is divided intopieces by dicing or the like to obtain pieces of printed circuit boards10 (see FIG. 50).

First Other Example of Second Modification of Third Embodiment

Next, a printed circuit board according to the first other example ofthe third embodiment will be described with reference to FIGS. 51 to 52.

FIG. 52 shows the printed circuit board according to the first otherexample. The printed circuit board according to the first other exampleis the same as the printed circuit board according to the secondmodification stated above with reference to FIG. 50. However, in thesecond modification stated above, the IC chips are contained in the coresubstrate 30 and then the transition layers 38 are formed. In the firstother example, by contrast, transition layers 38 are formed on IC chipsand then the IC chips are contained in a core substrate as in the caseof the first embodiment.

Next, description will be given to the method of manufacturing themultilayer printed circuit board according to the first other exampleshown in FIG. 52 constituted by containing semiconductor devices (or ICchips) 20A and 20B in the through holes of a core substrate, withreference to FIG. 51. Here, transition layers 38 are provided on the ICchips 20A and 20B in the same manner as the manufacturing method of thefirst embodiment described above.

(1) First, an insulating resin substrate (or core substrate) 30 in whichprepregs each having a core material made of glass cloths or the likeand impregnated with a resin such as epoxy are built up, is used as astarting material (see FIG. 51(A)). Next, recesses 32 for containing ICchips are formed on one side of the core substrate 30 by counter boring(see FIG. 51(B)). While the recesses are provided by counter boringherein, it is also possible to form a core substrate having containingsections by laminating an insulating resin substrate having openingportions and an insulating resin substrate without openings.(2) Then, an adhesive material 34 is applied to the recesses 32 using aprinting machine. At this time, potting instead of application may beconducted. Next, IC chips 20A and 20B are mounted on the adhesivematerial 34 (see FIG. 51(C)).(3) Then, the upper surfaces of the IC chips 20A and 20B are depressedor struck to thereby completely contain the IC chips 20A and 20B in therecesses 32 (see FIG. 51(D)). By doing so, the core substrate 30 can besmoothed. Since following steps are the same as those in the secondmodification described above with reference to FIGS. 47 to 49, nodescription will be given thereto.

In the third embodiment, by providing the transition layers on the diepads, it is possible to prevent resin residues on the pads and theconnection characteristics between the die pads and the via holes andreliability can be improved. Further, multiple multilayer printedcircuit boards provided with semiconductor devices are manufactured.Then, the substrate is cut into pieces and a plurality of multilayerprinted circuit boards are obtained. Due to this, it is possible toefficiently manufacture highly reliable multilayer printed circuitboards.

Moreover, compared with the conventional IC chip mounting method, thewiring length from the IC chip to the substrate to the externalsubstrate can be advantageously shortened and loop inductance can beadvantageously reduced.

Fourth Embodiment

The fourth embodiment according to the present invention will bedescribed hereinafter with reference to the drawings.

As shown in FIG. 57, a multilayer printed circuit board in the fourthembodiment comprises a core substrate 30 containing therein an IC chip20, an interlayer resin insulating layer 50 and an interlayer resininsulating layer 150. Via holes 60 and conductor circuits 58 are formedon the interlayer resin insulating layer 50. Via holes 160 and conductorcircuits 158 are formed on the interlayer resin insulating layer 150. Aradiating plate 44 is attached to the rear surface of the IC chip 20.

A solder resist layer 70 is provided on the interlayer resin insulatinglayer 150. Solder bumps 76 for connecting to an external substrate,which is not shown, such as a daughter board or a mother board areprovided on the conductor circuit 158 under the opening portions 71 ofthe solder resist layer 70.

As in the case of the first embodiment, die pads 22 and wirings (notshown) are provided on the upper surface of the IC chip 20, apassivation film 24 is covered on the die pads 22 and the wirings andthe openings of the passivation film 24 are formed in the respective diepads 22. Transition layers 38 mainly comprising copper are formed on therespective die pads 22. Each transition layer 38 comprises a thin filmlayer 33 and an electroplated film 37.

In case of the multilayer printed circuit board 10 in the fourthembodiment, the IC chip 20 is integrated into a core substrate 30 andthe transition layers 38 are provided on the respective pads 22 of theIC chip 20. Due to this, it is possible to connect the IC chip to themultilayer printed circuit board (or package substrate) electricallywithout using lead members and a sealing resin. Also, since thetransition layers 38 are formed on the IC chip portion, the IC chipportion is flattened and the upper interlayer resin insulating layer 50is flattened accordingly, thereby providing uniform film thickness.Further, the transition layers allow maintaining shape even if the uppervia holes 60 are formed.

Moreover, by providing the transition layers 38 made of copper on therespective die pads 22, it is possible to prevent resin residues on thedie pads 22 and to prevent the die pads 22 from being discolored ordissolved even after impregnating the multilayer printed circuit boardin an acid, an oxidizer or an etching solution in a later step orconducting various annealing steps. Thus, connection characteristicbetween the die pads of the IC chip and the via holes and reliabilitycan be improved. Furthermore, by interposing the transition layers 38each having a diameter of 60 μm or more on the respective pads 22 eachhaving a diameter of 40 μm, it is possible to ensure connecting the viaholes each having a diameter of 60 μm.

Next, the method of manufacturing the multilayer printed circuit boardaccording to the fourth embodiment will be described with reference toFIGS. 53 to 56.

(1) A core substrate 30 having the thickness of 0.5 mm, in whichprepregs each having a core material made of glass cloths or the likeand impregnated with a resin such as BT (Bismaleimide-Triazine) resin orepoxy are built up and cured, is used as a starting material. First, athrough hole 32 for containing therein an IC chip is formed in a coresubstrate 30 (see FIG. 53(A)). While the resin substrate 30 having thecore material impregnated with the resin is used herein, it is alsopossible to use a resin substrate without a core material. It ispreferable to provide tapers 32 a on the lower end opening portions ofthe through hole 32. By providing the tapers 32 a, no bubbles remainamong the IC chip 20, the filling resin 41 and the substrate 30 and thereliability of the multilayer printed circuit board can be improved.(2) Thereafter, a UV tape 40 is bonded to the bottom of the through hole32 of the core substrate 30 (see FIG. 53(B)). As this UV tape 40, anadhesive tape such as Adwill D-201, D-203, D2303DF, D-204, D210 or D210manufactured by LINTEC Corporation, which can be perfectly peeledbecause the bonding force of the adhesive surface of the tape is lost bybeing applied with UV, can be used. While the UV tape is used herein,various types of adhesive tapes, such as a polyimide tape, thestickiness of which does not lower at a high temperature of 80° C. ormore are available.(3) The IC chip 20 described above with reference to FIG. 3(B) is put onthe UV tape 40 on the through hole 32 formed in the core substrate 30 sothat die pads 38 contact with the surface to which the UV tape 40adheres (see FIG. 53(C)).(4) Filler 41 is filled into the through hole 32 formed in the coresubstrate 30 (see FIG. 53(D)). The filler 41 is filled by printing, maskprinting, potting or the like. As this filler, a resin having aviscosity of 0.1 to 50 Pa·s and obtained by mixing an imidazole, aminicor acid anhydride hardening agent or the like and filler (organicparticles, inorganic particles or metallic particles) as well as asolvent (such as a ketone solvent or a toluene solvent) at need in anepoxy resin, a polyimide resin or the like can be appropriately used. Asthe filler, a thermosetting resin, a thermoplastic resin or a mixturethereof can be used.(5) After filling the filler 41, the pressure of resultant substrate isreduced in a pressure reducing chamber for about 10 minutes to removebubbles in the filler 41. By doing so, no bubbles remain in the filler41 and the reliability of the multilayer printed circuit board can beimproved.(6) The core substrate 30 described above is pressurized from verticaldirection by stainless (SUS) press plates 100A and 100B for ten minutes(see FIG. 53(E)). Thereafter, while keeping pressure, the substrate isheated at 70° C. to 120° C. for about 30 minutes to thereby temporarilycure the filler 41. It is preferable that pressurization andpressurization and/or temporary curing are conducted under a reducedpressure atmosphere. By reducing pressure, no bubbles remain among theIC chip 20, the core substrate 30 and the filler 41 and in the filler 41and the reliability of the multilayer printed circuit board can beimproved. Since pressure is applied to the die pads 38 while the UV tape40 functions as a buffer during pressurization, the die pads 38 are notdamaged.(7) The UV tape 40 on the core substrate 30 having the filler 41temporarily cured is applied with UV to remove the adhesion of the tapeand then peeled (see FIG. 54(A)). Since the UV tape 40 is used in thefourth embodiment, no adhesive remains on the die pads 38 of the IC chipand the UV tape 40 can be perfectly peeled without damaging die pads 38.Due to this, it is possible to appropriately connect the via holes 60 tothe respective die pads 38 in a later step.(8) Thereafter, the filler 41 and the core substrate 30 on the rearsurface of the IC chip 20 are polished by belt sander polishing usingbelt abrasive paper (manufactured by Sankyo Chemical), thus exposing therear surface side of the IC chip 20 (see FIG. 54(B)). Since thepolishing is conducted in a state in which the filer 41 is temporarilycured in the fourth embodiment, the filler 41 and the core substrate 30can be easily polished.(9) Thereafter, heat is further applied to actually cure the filler 41,thereby forming a core substrate 30 containing therein the IC chip 20.This actual curing is preferably conducted under a reduced pressureatmosphere. By reducing pressure, no bubbles remain in the filler 41 andno grooves are formed. Besides, it is possible to improve thereliability and smoothness of the multilayer printed circuit board.(10) A radiating plate 44 is attached to the rear surface of the IC chip20 through a thermally conductive adhesive (e.g., a resin containingmetallic particles) 42 (see FIG. 54(C)). As the radiating plate, ametallic plate such as an aluminum or copper plate or a ceramic platecan be used. Since the bottom side of the core substrate 30 is polishedand the bottom of the IC chip 20 is exposed in the fourth embodiment, itis possible to attach the radiating plate 44 to the bottom of the ICchip and to improve the stability of the operation of the IC chip 20.(11) A thermosetting resin sheet having a thickness of 50 μm isvacuum-compression laminated onto the surface of the IC chip which hasgone through the above-stated steps at a pressure of 5 kg/cm² whileraising temperature to 50 to 150° C., thereby providing an interlayerresin insulating layer 50 (see FIG. 54(D)). The degree of vacuum at thetime of vacuum compression is 10 mmHg.(12) Next, using CO₂ gas laser having a wavelength of 10.4 μm, via holeopenings 48 each having a diameter of 60 μm are provided in theinterlayer resin insulating layer 50 under the conditions of a beamdiameter of 5 mm, a top hat mode, a pulse width of 5.0 sec., a mask holediameter of 0.5 mm and one shot (see FIG. 54(B)). Using an oxidizer suchas a chromium acid or a permanganic acid, resin residues in the openings48 are removed. By providing the transition layer 38 made of copper oneach die pad 22, it is possible to prevent resin residues on the die pad22, thereby improving connection characteristic between the die pad 22and the via hole 60 to be described later and improving reliability.Furthermore, by interposing the transition layer 38 having a diameter of60 μm or more on the die pad 22 having a diameter of 40 μm, it ispossible to ensure connecting the via hole opening 48 having a diameterof 60 μm. While the resin residues are removed by using the oxidizer, ade-smear process can be also conducted using oxygen plasma.(13) Next, the resultant substrate is immersed in an oxidizer, such as achromic acid or a permanganic acid, or the like, thereby providing therough surface 50α of the interlayer resin insulating layer 50 (see FIG.55(A)). The rough surface 50 a is preferably formed in the range of 0.1to 5 μm. For example, the substrate is immersed in 50 g/l of a sodiumpermanganate solution at a temperature of 60° C. for 5 to 25 minutes,thereby providing a rough surface 50α of 2 to 3 μm. Alternatively, byperforming a plasma process, a rough surface 50α can be formed on thesurface of interlayer resin insulating layer 50.(14) A metallic layer 52 is provided on the interlayer resin insulatinglayer 50 on which the rough surface 50α has been formed (see FIG.55(B)). The metallic layer 52 is formed by electroless plating. Bysupplying a catalyst such as a palladium catalyst to the surface layerof the interlayer resin insulating layer 50 in advance and immersing thesubstrate into an electroless plating solution for 5 to 60 minutes, themetallic layer 52 which is a plated film in the range of 0.1 to 5 μm isprovided.

Alternatively, an Ni/Cu metallic alloy 52 can be formed on the surfaceof the interlayer resin insulating layer 50 using the same device asthat used for the above-stated plasma process.

(15) A commercially available photosensitive dry film is bonded to thesubstrate 30 which has gone through the above processes, a photomaskfilm is mounted, exposure is performed at 100 mj/cm² and then adevelopment process is conducted with 0.8% sodium carbonate, therebyproviding a plating resist 54 having a thickness of 15 μm. Next,electroplating is conducted under the same conditions as in the firstembodiment to thereby form an electroplated film 56 having a thicknessof 15 μm (see FIG. 55(C)).(16) After peeling and removing the plating resist 54 with 5% NaOH, themetallic layer 52 under the plating resist is dissolved and removed byetching using a mixture solution of a nitric acid, a sulfuric acid and ahydrogen peroxide, conductor circuits 58 each comprising the metalliclayer 52 and the electroplated film 56 and having a thickness of 16 μmand via holes 60 are formed and rough surfaces 58α and 60α are formedusing an etching solution containing a cupric salt complex and anorganic acid (see FIG. 55(D)). In the fourth embodiment, as stated abovewith reference to FIG. 53(E), the surface of the core substrate 30 isformed completely smoothly, so that the IC chip 20 can be appropriatelyconnected to the transition layers 38 through the via holes 60. Due tothis, the reliability of the multilayer printed circuit board can beimproved.(17) Next, the steps of (6) to (11) stated above are repeated, therebyforming an upper interlayer resin insulating layer 150 and conductorcircuits 158 (including via holes 160) (see FIG. 56(A)).(18) Then, the solder resist composition (or organic resin insulatingmaterial) prepared in the same manner as that in the first embodiment isobtained.(19) Next, the above-stated solder resist composition is applied to thesubstrate 30 to have a thickness of 20 μm and a drying process isconducted at 70° C. for 20 minutes and 70° C. for 30 minutes. Then, aphotomask having a pattern of solder resist opening portions drawnthereon and a thickness of 5 mm is made hermetic contact with the solderresist layer 70, exposure is performed with ultraviolet rays with 1000mj/cm² and then a development process is performed with a DMTG solution,thereby developing by DMTG solution, and forming openings 71 each havinga diameter of 200 μm (see FIG. 56(B)).(20) Next, a nickel plated layer 72 having a thickness of 5 μm is formedon each opening portion 71 of the substrate on which the solder resistlayer (or organic resin insulating layer) 70 has been formed. Further, agold plated layer 74 having a thickness of 0.03 μm is formed on thenickel plated layer 72, thereby forming solder pads 75 on the respectiveconductor circuits 158 (see FIG. 56(C)).(21) Thereafter, a solder paste is printed on the opening portions 71 ofthe solder resist layer 70 and reflow is conducted at 200° C., therebyforming solder bumps 76. As a result, it is possible to obtain amultilayer printed circuit board 10 into which the IC chip 20 isintegrated and which has the solder bumps 76 (see FIG. 57).

In the fourth embodiment, the IC chip 20 is mounted so that the die pads38 contact with the UV tape 40, the UV tape 40 is peeled and then thebuildup layers are formed on the IC chip 20. Due to this, it is possibleto appropriately, electrically connect the IC chip to the via holes 60of the buildup layers and to manufacture a highly reliable multilayerprinted circuit board into which a semiconductor device is integrated.

As stated above, according to the fourth embodiment, the semiconductordevice is mounted on the sheet at the bottom of the through hole of thecore substrate so that terminals contact with the sheet, the sheet ispeeled after the resin is filled into the through hole and the builduplayers are formed. Namely, the semiconductor device is mounted on thesheet so that the terminals contact with the sheet and the builduplayers are formed on the semiconductor device after peeling the sheet.Thus, it is possible to appropriately, electrically connect theterminals to the wirings of the buildup layers and to manufacture ahighly reliable multilayer printed circuit board into which thesemiconductor device is integrated.

Fifth Embodiment

The fifth embodiment of the present invention will be describedhereinafter.

The constitution of a multilayer printed circuit board according to thefifth embodiment will be described with reference to FIG. 63 which showsthe cross section of a multilayer printed circuit board 10.

As shown in FIG. 63, the multilayer printed circuit board 10 comprises acore substrate 30 containing therein an IC chip 20, an interlayer resininsulating layer 50, an interlayer resin insulating layer 150 and aninterlayer resin insulating layer 250. Via holes 60 and conductorcircuits 58 are formed on the interlayer resin insulating layer 50. Viaholes 160 and conductor circuits 158 are formed on the interlayer resininsulating layer 150. Via holes 260 and conductor circuits 258 areformed on the interlayer resin insulating layer 250.

A solder resist layer 70 is provided on the interlayer resin insulatinglayer 250. BGA's 76 for connecting to an external substrate, not shown,such as a daughter board or a mother board, are provided on theconductor circuits 258 under the respective opening portions 71 of thesolder resist layer 70. The BGA's 76 are provided in a region R2 otherthan a region R1 right above the IC chip 20.

The IC chip 20 is covered with a passivation film 24 protecting the ICchip 20 and die pads 22 each constituting an input/output terminal areprovided in the respective openings of the passivation film 24.Transition layers 38 mainly comprising copper are formed on therespective pads 22.

An adhesive material 34, which is a resin material, is filled betweenthe IC chip 20 and the recess 32 of the substrate 30. The adhesivematerial 34 allows the IC chip 20 to be fixed in the recess of thesubstrate 30. Since this resin filler material 34 relaxes a stressgenerated by thermal expansion, it is possible to prevent the crackingof the core substrate 30 and the waviness of the interlayer resininsulating layers 50, 150 and 250 and the solder resist layer 70. Due tothis, it is possible to prevent peeling and cracking from occurring tothe surroundings of the BGA's 76. It is possible to prevent thedetachment and positional error of the solder bumps 76, accordingly. Itis, therefore, possible to improve electrical connection characteristicsand reliability.

FIG. 65 shows the cross-sectional view of the multilayer printed circuitboard 10 taken along line E-E of FIG. 63. An inside region denoted by adotted line in FIG. 65 is a region R1 into which the IC chip 20 isintegrated. A region outside of the dotted line and inside of a solidline in FIG. 65 is a region R2 into which the IC chip 20 is notintegrated. The conductor circuits 258 are formed to radially spreadfrom the region R1 to the region R2. The solder pads 75 to be connectedto the BGA's 76, respectively, are arranged in the region R2 in agrid-like fashion.

FIG. 66(A) is a plan view of the multilayer printed circuit board 10shown in FIG. 63. The BGA's 76 are arranged in the region R2 in agrid-like fashion and connected to the external substrate, not shown,such as a daughter board or a mother board. The BGA's 76 may be formedin the region R2 in a staggered fashion as shown in FIG. 66(B).

In case of the multilayer printed circuit board in the fifth embodiment,the BGA's 76 are provided in the region R2 on the substrate into whichregion the IC chip is not integrated.

That is, by providing the BGA's 76 in the region R2 other than theregion right above the IC chip 20, it is possible to reduce theinfluence of the thermal expansion of the IC chip 20 made of ceramic andhaving a low coefficient of thermal expansion and the interlayerinsulating layers 50, 150, 250 and the solder resist layer 70 each ofwhich is made of resin and has a high coefficient of thermal expansionand, therefore, possible to prevent peeling and cracking from occurringto the surroundings of the BGA's 76 and the like. Accordingly, it ispossible to prevent the detachment and positional error of the solderbumps 76 and to improve electrical connection characteristics andreliability.

In the multilayer printed circuit board 10 in this embodiment, the ICchip 20 is integrated into the core substrate 30 and the transitionlayers 38 are provided on the respective pads 22 of the IC chip 20. Dueto this, it is possible to electrically connect the IC chip to themultilayer printed circuit board (or package substrate) without usinglead members and a sealing resin. Further, since the transition layers38 are formed on the IC chip portion, the IC chip portion is flattenedand the upper interlayer insulating layer 50 is, therefore, flattened tothereby provide uniform film thickness. Further, because of thetransition layers, it is possible to maintain the stability of shapeeven if the via holes 60 provided in the upper layer are formed.

Furthermore, by providing the transition layers 38 made of copper on therespective die pads 22, it is possible to prevent resin residues on thedie pads 22 and to prevent the die pads 22 from being discolored ordissolved even after impregnating the multilayer printed circuit boardin an acid, an oxidizer or an etching solution in a later step orconducting various annealing steps. Thus, connection characteristicbetween the die pads of the IC chip and the via holes and reliabilitycan be improved. Besides, by interposing the transition layers 38 eachhaving a diameter of 60 μm or more on the respective pads 22 each havinga diameter of 40 μm, it is possible to ensure connecting the via holeseach having a diameter of 60 μm.

Next, the method of manufacturing the multilayer printed circuit boardin the fifth embodiment described above with reference to FIG. 63 willbe described with reference to FIGS. 58 to 62.

(1) First, an insulating resin substrate (or a core substrate) 30 inwhich prepregs each having a core material made of glass cloths or thelike and impregnated with a resin such as epoxy are built up, isprepared as a starting material (see FIG. 58(A)). Next, a recess 32 forcontaining therein an IC chip is formed on one side of the coresubstrate 30 by counter boring (see FIG. 58(B)). While the recess isprovided by counter boring herein, it is also possible to form a coresubstrate having a containing section by building up an insulating resinsubstrate having an opening to an insulating resin substrate without anopening.

As the resin substrate into which an electronic component such as an ICchip is integrated, a resin such as an epoxy resin, a BT resin, a phenolresin or the like impregnated with a reinforcement or a core materialsuch as a glass epoxy resin, a substrate in which prepregs impregnatedwith an epoxy resin are built up, or the like is used. Normally, asubstrate used for a printed circuit board can be used. Alternatively, atwo-sided copper-clad laminated board, a one-side board, a resin boardwhich does not include a metallic film or a resin film can be used. Itis noted, however, a resin is resolved and carbonated if heated at atemperature of 350° C. or higher.

(2) Thereafter, an adhesive material 34 is applied to the recess 32using a printing machine. At this time, potting instead of applicationmay be conducted. Next, an IC chip 20 according to the manufacturingmethod of the first embodiment is mounted on the adhesive material 34(see FIG. 58(C)). As the adhesive material 34, a resin having a highercoefficient of thermal expansion than that of the core substrate 30 isused. Such an adhesive material absorbs the difference in thermalexpansion between the IC chip 20 and the core substrate 30.(3) Then, the upper surface of the IC chip 20 is depressed or struck tothereby completely contain the IC chip 20 in the recess 32 (see FIG.58(D)). By doing so, the core substrate 30 can be smoothed. At thismoment, the adhesive material 34 is sometimes applied on the uppersurface of the IC chip 20. However, as described later, since resinlayers are provided on the upper surface of the IC chip 20 and thenopenings for via holes are provided by laser, the adhesive material 34does not influence the connection between transition layers 38 and viaholes.(4) A thermosetting resin sheet having a thickness of 50 μm isvacuum-compression laminated onto the substrate 30 which has gonethrough the above-stated steps at a pressure of 5 kg/cm² while raisingtemperature to 50 to 150° C., thereby providing an interlayer resininsulating layer 50 (see FIG. 59(A)). The degree of vacuum at the timeof vacuum compression is 10 mmHg.

Also, the interlayer resin insulating layer 50 can be formed by applyinga resin composition the viscosity of which has been adjusted in advanceby a roll coater or a curtain coater instead of forming the semi-curedresin into a film shape to heat-compress as stated above.

(5) Next, using CO₂ gas laser having a wavelength of 10.4 μm, via holeopenings 48 each having a diameter of 60 μm are provided in theinterlayer resin insulating layer 50 under the conditions of a beamdiameter of 5 mm, a top hat mode, a pulse width of 5.0 microseconds, amask hole diameter of 0.5 mm and one shot (see FIG. 59(B)). Using apermanganic acid at a temperature of 60° C., resin residues in theopenings 48 are removed. By providing a transition layer 38 made ofcopper on each die pad 22, it is possible to prevent resin residues onthe pad 22, thereby improving connection characteristic between the pad22 and a via hole 60 to be described later and improving reliability.Furthermore, by interposing the transition layer 38 having a diameter of60 μm or more on the die pad 22 having a diameter of 40 μm, it ispossible to ensure connecting the via hole opening 48 having a diameterof 60 μm. While the resin residues are removed by using a permanganicacid, a de-smear process can be also conducted using oxygen plasma.(6) Next, the resultant substrate is immersed in an oxidizer, such as achromic acid or a permanganic acid, or the like, thereby providing therough surface 50α of the interlayer resin insulating layer 50 (see FIG.59(C)). The rough surface 50 α is preferably formed to have a thicknessin the range of 0.05 to 5 μm. For example, the substrate is immersed in50 g/l of a sodium permanganate solution at a temperature of 60° C. for5 to 25 minutes, thereby providing a rough surface 50α of 2 to 3 μm.Alternatively, by performing a plasma process, the rough surface 50α canbe formed on the surface of interlayer resin insulating layer 50.(7) A metallic layer 52 is provided on the interlayer resin insulatinglayer 50 on which the rough surface 50α has been formed (see FIG.60(A)). The metallic layer 52 is formed by electroless plating. Bysupplying a catalyst such as a palladium catalyst to the surface layerof the interlayer resin insulating layer 50 in advance and immersing thesubstrate into an electroless plating solution for 5 to 60 minutes as inthe first embodiment, the metallic layer 52, which is a plated film, isprovided in the range of 0.1 to 5 μm.

Alternatively, an Ni/Cu metallic layer 52 can be formed on the surfaceof the interlayer resin insulating layer 50 using the same device asthat used in the above-stated plasma process. The metallic film can beformed by deposition, electro-deposition or the like instead ofsputtering. It is also possible to form a thin layer by a physicalmethod such as sputtering, deposition or electro-deposition and to thenconduct electroless plating.

(8) A commercially available photosensitive dry film is bonded to thesubstrate 30 which has been subjected to the above process, a photomaskfilm is mounted, exposure is conducted at 100 mj/cm² and then adevelopment process is conducted with 0.8% sodium carbonate, therebyproviding a plating resist 54 having a thickness of 15 μm (see FIG.60(B)). Then, electroplating is conducted under the same conditions asthose in the first embodiment, thereby forming an electroplated film 56having a thickness of 15 μm (see FIG. 60(C)).(9) After peeling and removing the plating resist 54 with 5% NaOH, themetallic layer 52 under the plating resist is dissolved and removed byetching using a mixture solution of a nitric acid, a sulfuric acid andhydrogen peroxide, conductor circuits 58 each comprising the metalliclayer 52 and the electroplated film 56 and having a thickness of 16 μmand via holes 60 are formed (see FIG. 61(A)). As the etching solution,cupric chloride, ferric chloride, persalt, hydrogen peroxide/sulfuricacid, alkaline etchant or the like can be used. Next, using an etchingsolution containing cupric complex, and organic acid, rough surfaces 58αand 60α are formed (see FIG. 61(B)).(10) Next, the steps of (7) to (12) stated above are repeated, therebyforming an interlayer resin insulating layer 150 and conductor circuits158 (including via holes 160) are formed on the upper layer of theinterlayer resin insulating layer 50 and an interlayer resin insulatinglayer 250 and conductor circuits 258 (including via holes 260) (see FIG.61(C)).(11) Next, a solder resist composition prepared in the same manner asthat in the first embodiment is obtained.(12) Next, the solder resist composition is applied to the substrate 30to have a thickness of 20 μm and a drying process is conducted. Then, aphotomask is made hermetic contact with the solder resist layer 70,exposure and then a development process are performed, thereby formingopenings 71 each having a diameter of 200 μm (see FIG. 62(A)).(13) Next, a nickel plated layer 72 having a thickness of 5 μm is formedon each opening portion 71 of the substrate on which the solder resistlayer (or organic resin insulating layer) 70 has been formed. Further, agold plated layer 74 having a thickness of 0.03 μm is formed on thenickel plated layer 72, thereby forming a solder pad 75 on eachconductor circuit 258 (see FIG. 62(B)).(14) Thereafter, a solder paste is printed on the opening portions 71 ofthe solder resist layer 70. As the solder paste, Sn/Pb, Sn/Sb, Sn/Ag,Sn/Ag/Cu or the like may be used. A solder paste of low α radiation raytype may be used. Next, reflow is conducted at 200° C., thereby formingBGA's 76 in the region R2 into which the IC chip 20 is not integrated ina grid-like fashion (or a staggered fashion) (see FIGS. 63, 66(A) and66(B)). As a result, it is possible to obtain a multilayer printedcircuit board 10 into which the IC chip 20 is integrated and which hasthe BGA's 76 (see FIG. 63). It is noted that the IC chip 20 may bearranged in a deviated position instead of the central portion of thesubstrate 30. In FIG. 63, the BGA's are arranged as external connectionterminals. As shown in FIG. 64, even if PGA's 96 are attached asexternal connection terminals, it is preferably that the PGA's areprovided in the region R2 into which the IC chip 20 is not integrated.

Other Example of Fifth Embodiment

Next, description will be given to a multilayer printed circuit boardaccording to the other example of the fifth embodiment. In the fifthembodiment stated above, the via holes are formed in the interlayerresin insulating layers using laser. In this example, by contrast, viaholes are formed by exposure. The method of manufacturing a multilayerprinted circuit board according to the other example will be describedwith reference to FIG. 67.

(4) As in the case of the fifth embodiment, a thermosetting epoxy resin51 having a thickness of 50 μm is applied to the substrate 30 which hasgone through the steps (1) to (3) described above (see FIG. 67(A)).

(5) Next, a photomask film having black circles corresponding to viahole formed positions drawn thereon is put on the interlayer resininsulating layer 50 and exposure is conducted. Then, development isconducted by spraying a DMTG solution and a heat process is conducted,thereby providing openings 48 each having a diameter of 85 μm for viaholes (see FIG. 67(B)).(6) The surface of the interlayer resin insulating layer 50 is roughenedwith a permanganic acid or a chromic acid, thereby forming a roughsurface 50α (see FIG. 67(C)). The thickness of the rough surface 50α ispreferably in the range of 0.05 to 5 μm. Since following steps are thesame as those in the fifth embodiment stated above, no description willbe given thereto.

First Modification of Fifth Embodiment

Next, the method of manufacturing a multilayer printed circuit boardaccording to the first modification will be described with reference toFIGS. 68 to 70. In the fifth embodiment stated above, the transitionlayers 38 are formed on the IC chip 20 and then the IC chip 20 iscontained in the core substrate 30. In the first modification, bycontrast, an IC chip is contained in a core substrate and thentransition layers are formed.

(1) First, an insulating resin substrate (or core substrate) 30 in whichprepregs each having a core material made of glass cloths or the likeand impregnated with a resin such as epoxy are built up, is prepared asa starting material (see FIG. 68(A)). Next, a recess 32 for containingtherein an IC chip is formed on one side of the core substrate 30 bycounter boring (see FIG. 68(B)).(2) Thereafter, an adhesive material 34 is applied to the recess 32using a printing machine. At this time, potting instead of applicationmay be conducted. Next, an IC chip 20 is mounted on the adhesivematerial 34 (see FIG. 68(C)).(3) Then, the upper surface of the IC chip 20 is depressed or struck tothereby completely contain the IC chip 20 in the recess 32 (see FIG.69(A)). By doing so, the core substrate 30 can be smoothed.(4) Thereafter, the entire surface of the core substrate 30 whichcontains the IC chip 20 therein is subjected to physical deposition suchas deposition or sputtering to thereby form a conductive metallic layer33 on the entire surface (FIG. 69(B)). The metallic film may bepreferably formed out of one or more metallic layers made of tin,chromium, titanium, nickel, zinc, cobalt, gold or copper or the like.The thickness thereof is preferably in the range of 0.001 to 2.0 μm,more preferably, 0.01 to 1.0 μm.

A plated film 36 may be formed on the metallic film 33 by electrolessplating (see FIG. 69(C)). The types of plating materials include copper,nickel, gold, silver, zinc, iron and the like. In view of electricalcharacteristics, inexpensiveness and the fact that a buildup conductorlayer to be formed in a later step mainly comprises copper, copper ispreferably used. The thickness thereof is preferably in the range of 1to 20 μm.

(5) Thereafter, a resist is applied, exposure and development areconducted to provide a plating resist 35 so as to provide openings onthe upper portions of the respective die pads 22 of the IC chip 20, andelectroless plating is conducted to thereby provide an electrolessplated film 37 (see FIG. 70(A)). After removing the plating resist 35,the electroless plated film 36 and the metallic film 33 under theplating resist 35 are etched away, thereby forming transition layers 38on the respective die pads 22 of the IC chip (see FIG. 70(B)). While thetransition layers are formed by the plating resist herein, thetransition layers 38 may be formed on the respective die pads 22 of theIC chip 20 by, after uniformly forming an electroplated film on theelectroless plated film 36, forming an etching resist, conductingexposure and development to expose the metal other than that of thetransition layers 38, and conducting etching. The thickness of theelectroplated film is preferably in the range of 1 to 20 μm. If thethickness exceeds that range, undercut may possibly occur during theetching to generate gaps in the interfaces between the transition layersto be formed and the via holes.(6) Next, an etching solution is sprayed onto the substrate and thesurfaces of the transition layers 38 is etched, thereby forming roughsurfaces 38α (see FIG. 70(C)). Since following steps are the same asthose in the fifth embodiment, no description will be given thereto.

Comparison Example 3

A multilayer printed circuit board according to comparison example 3will be described. In the fifth embodiment stated above, the BGA's 76are arranged in the region R2 other than the region right above the ICchip. In the comparison example 3, by contrast, BGA's 76 are uniformlyarranged on a solder resist layer as shown in FIG. 66(C). Namely, theBGA's 76 are formed on the entire surface of the solder resist layer ina grid-like (or full grid-like) fashion without differentiating a regionR1 from a region R2.

After connecting the multilayer printed circuit board according to thefifth embodiment and the multilayer printed circuit board according tothe comparison example 3 to external substrates, respectively, theboards were electrically connected to the respective external substrateand the following items were estimated:

(a) Whether or not cracking and/or peeling occurred after mounting themultilayer printed circuit board onto the external substrate.

(b) Whether or not BGA's defects occurred.

(c) Whether or not cracking and/or peeling occurred after mounting themultilayer printed circuit board onto the external substrate after areliability test.

(d) Whether or not BGA's defects occurred after the reliability test.

(e) Measurement of contact resistance.

The multilayer printed circuit board according to the fifth embodimentshowed an appropriate result. In case of the comparison example 3,however, cracking and/or peeling was found in the surroundings of theBGA's. Also, it was found that the contact resistance increased. Thesame results were obtained if PGA's instead of the BGA's as shown inFIG. 64 were used.

As stated above, according to the fifth embodiment, the region on thesubstrate into which region the semiconductor device of the multilayerprinted circuit board is integrated and the region on the substrate intowhich region the semiconductor device is not integrated aredifferentiated from each other. Then, the external connection terminals(BGA's/PGA's) are arranged in the region on the substrate into whichregion the semiconductor device is not integrated. Namely, by arrangingthe external connection terminals (BGA's/PGA's) in the region on thesubstrate into which region the semiconductor device is not integrated,the influence of thermal expansion can be reduced and peeling and/orcracking can be, therefore, prevented from occurring to the surroundingsof the external connection terminals (BGA's/PGA's). Accordingly, it ispossible to prevent the detachment or positional error of the externalconnection terminals (BGA's/PGA's) and to improve electrical connectioncharacteristics and reliability.

1. A method of manufacturing a printed circuit board, comprising:providing a core substrate having a first surface and a second surfaceon an opposite side of the first surface; forming a through hole throughthe core substrate for accommodating an electronic device having aterminal; covering the through hole of the core substrate with anadhesive tape from the second surface of the core substrate; putting theelectronic device in the through hole of the core substrate such thatthe terminal of the electronic device adheres to the adhesive tape;removing the adhesive tape from the second surface of the coresubstrate; forming an insulating layer over the second surface of thecore substrate; forming a via hole opening connected to the terminal ofthe electronic device; forming a conductive circuit over the insulatinglayer; and forming a via hole structure in the via hole opening in theinsulating layer so as to establish electrical connection between theconductive circuit and the terminal of the electronic device.
 2. Themethod of manufacturing a printed circuit board according to claim 1,further comprising filling a filler into the through hole of the coresubstrate.
 3. The method of manufacturing a printed circuit boardaccording to claim 2, further comprising polishing at least one of thefirst surface and second surface of the core substrate after the fillingof the filler into the through hole of the core substrate.